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Olympic 914
Took the car out for a drive today, planning on going to dinner. everything is working as it should. getting on the PA turnpike and I had to accelerate briskly to get into traffic, and a moment later I noticed that the RED alternator light had come on. Pulled of at a wide spot to check the belt and wires and shut it off. Not checking the belt with it running. Belt good, plug tight, tapped the VR a couple times for good measure and started it back up. Light still on and now my Autometer AFR gauge just had bars. I know that is because it doesn't turn on until the voltage is +13v So not charging.

Now I am on a limited access highway with the next exit `12-15 miles away. Good thing had the battery fully charged on the tender before I left the house. So I made it to the next exit, turned around and headed back home for a total of 35 miles on battery only. Whew. But that shot dinner.....



Replace the VR with another I had that previously tested good. still no charging. checked the plug on the relay plate again. looks good.

I have not yet checked the wire connections at the alternator, possibly a wire vibrated loose during the brisk acceleration.

Now the question

I read to test the VR to short between D+ and DF and if the alternator is good voltage at the battery will go to alternator maximum of about 15-16V

So do I REMOVE the VR for this test? and jump between the D+ and DF at the relay plate.
OR
Leave the VR in place and short between those pins?
Spoke
QUOTE(Olympic 914 @ Mar 25 2018, 07:05 PM) *

Took the car out for a drive today, planning on going to dinner. everything is working as it should. getting on the PA turnpike and I had to accelerate briskly to get into traffic, and a moment later I noticed that the RED alternator light had come on. Pulled of at a wide spot to check the belt and wires and shut it off. Not checking the belt with it running. Belt good, plug tight, tapped the VR a couple times for good measure and started it back up. Light still on and now my Autometer AFR gauge just had bars. I know that is because it doesn't turn on until the voltage is +13v So not charging.

Now I am on a limited access highway with the next exit `12-15 miles away. Good thing had the battery fully charged on the tender before I left the house. So I made it to the next exit, turned around and headed back home for a total of 35 miles on battery only. Whew. But that shot dinner.....



Replace the VR with another I had that previously tested good. still no charging. checked the plug on the relay plate again. looks good.

I have not yet checked the wire connections at the alternator, possibly a wire vibrated loose during the brisk acceleration.

Now the question

I read to test the VR to short between D+ and DF and if the alternator is good voltage at the battery will go to alternator maximum of about 15-16V

So do I REMOVE the VR for this test? and jump between the D+ and DF at the relay plate.
OR
Leave the VR in place and short between those pins?


Yes, disconnect only the VR. Jump the D+ and DF pins. See diagram below. Shorting D+ and DF will provide maximum voltage to the armature and thus maximum alternator output.

Only do this test in short bursts as this stresses the alternator and battery to the max.
Olympic 914
QUOTE(Spoke @ Mar 26 2018, 09:21 AM) *



Yes, disconnect only the VR. Jump the D+ and DF pins. See diagram below. Shorting D+ and DF will provide maximum voltage to the armature and thus maximum alternator output.

Only do this test in short bursts as this stresses the alternator and battery to the max.


OK did this test. Removed the VR and placed a jumper wire between D+ and DF on the relay plate. had a Multi tester hooked up and started the engine. tester showed voltage go to 15 , 16 and end around 17V when I shut if off.

so the alternator is good.

Now it gets weird. Plugged one of the voltage regulators back in and now its charging. battery is 12.8 at rest. ( fully charged it last night) and goes to 13.4 running, Gen light goes off. Tried the other VR and same result, but voltage only goes to 13.3

Maybe a bad connection? wires from alternator to plug look good.

I think I will order a new VR anyways. its easy to change....
falcor75
Ground cable between gearbox and chassi?
Olympic 914
QUOTE(falcor75 @ Mar 26 2018, 10:47 AM) *

Ground cable between gearbox and chassi?


New, Cleaned and connected.

Also B+ connection from alternator to starter checked and tight.

Didn't check connections at alternator since you can't get to them with alternator in car. (not easily at least )
Mikey914
Well if all works well great. I'd try driving it locally a bit.

There is a possibility that you have brushes are going out.

Put it under load (lights on) and drive it for about a half hour. It's rare when something is magically "fixed". Do also look for discoloration from heat on the harness, as this could indicate some damage making connection intermittently.

And by the way you CAN pull the alternator with the engine in the car. It's not bad as long as the screws are not stuck.
Olympic 914
QUOTE(Mikey914 @ Mar 26 2018, 11:40 AM) *

Well if all works well great. I'd try driving it locally a bit.

There is a possibility that you have brushes are going out.

Put it under load (lights on) and drive it for about a half hour. It's rare when something is magically "fixed".


I will be heading out to do that now. Will carry a multi-tester when I go. Need to get one of those Jump-start boxes just in case.

The alternator was also new when I put it back together, so it has about 2K miles on it now. I understand that doesn't rule it out as a possible problem though. the tail and turn signals are LEDs (Thanks Spoke) and the headlights are Trucklite LEDs. I was trying to lessen the load on the alternator when I put it all back together.
Olympic 914
So this alternator problem continues to vex me.

tested it by jumping DF and D+ and had good voltage, also tested jumping 12V to DF and also had good voltage. by these tests I ASSUMED the alternator was OK.

it was a rebuilt Bosch AL75X with 2k miles on it.

I just had the engine out for a leaking galley plug and while there replaced the alternator wiring harness with a new one from Bowlsby. I had the Fuching alternator in my hands......

Now during another 300 mile trip the Alt light came on at a about.250 miles. I was stuck in the mother of all traffic jams when I noticed the alt had quit. Not too worried about getting home since I had brought my new jump-box along. but it made it. Stopped for a few minutes at a truck stop about 15 mile from home and when leaving there the alternator started charging again. I had noticed the regulator was very hot and I replaced it with the new Beru unit.

Took it out today for a little 40 mile ride and every thing was fine, decide to take the GF for a ride and before I get out of the driveway..... you guessed it, alt not charging.

Checked the bulb, checked the fuses, ground strap connected, try different relay plate. etc. etc. Ad Nauseam .......

this time when jumping DF and D+ I get NO charge, jump 12V to DF and get 14V

I guess one of the diodes in the alternator gave up the ghost. So now I think the alternator may have been intermittently going. confused24.gif ar15.gif And I had it in my hand.....

I was really working hard to bring this thing to Hershey, but other than bringing it on a trailer it has me beat..

Next step will be to pull the alternator and probably order a new one. Shit...
McMark
Dying relay board?
Olympic 914
QUOTE(McMark @ Apr 19 2018, 07:30 AM) *

Dying relay board?


I did hook up another relay board I had, and got the same result.

I saw your tutorial on removing the alternator and will be following that. Along with one I found on the Bird board.

To add to the complexity I do have HE and aux blower.
malcolm2
I have had some ALT probs too. Spoke must keep that how-to and photo on a virtual clip board. piratenanner.gif piratenanner.gif

They seemed to be re-builder problems. The last issue left me stranded. I watched my volt gauge drop and drop and drop to about 8.5 and that was it. Thank goodness I was in a Cracker Barrel parking lot. piratenanner.gif

Once I dis-assembled the ALT I found what might have been my issue. One of the brushes was not completely centered and 1/8" of it was not wearing down and it was extending in between the 2 copper rings.

I believe the brush was touching something it was not supposed to. anyway here is a photo from my thread.

My ALT Thread

I have a 75 and the HE do make it impossible to get the ALT out. I removed my AUX blower, hell that thing really did not do anything anyway. blink.gif I am getting pretty good at removing and installing the ALT now, but what a pain, and all the pieces and parts and sheet metal etc.... What a pain.

Best answer is to buy the best ALT you can and hope it never goes out again.
McMark
I think malcolm2 is right -- and I don't think even Bosch rebuilds are immune. That's one of the reasons I ended up doing an alternator swap using a new manufactured alternator from a company with a good reputation.
malcolm2
QUOTE(Olympic 914 @ Apr 18 2018, 08:20 PM) *


Next step will be to pull the alternator and probably order a new one. Shit...


If you have a rebuilder in your area, maybe they can check yours out and be very careful with it if you go in with some 914world knowledge. Maybe they have some good Google or Yelp reviews.....? Might only take a day vs. getting a questionable re-built one from an assembly line rebuilder in a week.

I say all that only to also say, my last dead ALT came from a mom and pop rebuilder. Turns out Jr was the rebuilder. He knows how to put them together and paint them, but probably is not quite there on the how-and-why skills, especially on these 45 YO alternators. I was the guinea pig.

The unit on my car now was also rebuilt by Jr. at the same time that my dead one. Only $38 bucks each, so I was happy until I had to get a ride home from Cracker Barrel. bootyshake.gif
malcolm2
I am bored today. Hey Spoke, how is this???

Click to view attachment
Olympic 914
There is also this.

I performed the tests below the red line.


There are four connections to the alternator itself. D+, DF,D-, and B+. If you look at the Haynes book, what is not readily apparent, but is true nevertheless, is that the set of diodes that connect to the D+ terminal are a duplicate set (except for lower curent rating) to the ones for the B+ terminal, which is the actual high current output of the alternator. The D+ terminal is therefore a duplicate output terminal of the alternator, with less current capability. The lower set of diodes on current track 80 is common to both the D+ and B+ functions, and forms the ground return for both the B+ and D+ outputs. The DF or "Dynamo Field" terminal connects to the ungrounded end of the alternator field winding, and is an input to the alternator. The current supplied to the DF terminal determines the strength of the magnetic field that penetrates the output windings, and thus controls the alternator's output. The D- terminal is connected to the alternator frame, and is the ground return for the voltage regulator. The other end of the field winding is also connected to ground at this point.
The Bosch alternator is incapable of self-excitation, or "boot-strapping" itself to an operating condition. Older DC generators and some U.S. alternators have residual magnetism retained in the core, or some other scheme to get enough field current to get themselves up and running. The Bosch alternator uses a different scheme. The charge warning lamp is connected between the ignition switch and the D+ terminal. When the car is first started, there is no output from the alternator at either the B+ or D+ terminals. The voltage regulator, sensing no output, is attempting to command maximum field current... it effectively shorts the D+ and DF terminals together. This places the D+ terminal close to ground potential, because the resistance of the field winding is not large. This means that there is +12 volts on one side of the charge warning lamp, and the other side of the lamp is grounded through the alternator field winding. Current thus flows through the lamp, lighting it. This same current, however, also flows through the alternator field winding, producing a magnetic field. This magnetic field is what the alternator needs to start up, and if everything is working correctly, that's exactly what happens. The alternator now begins to develop identical voltages at the D+ and B+ terminals. The D+ terminal is connected to one end of the charge warning lamp, while the other end of the lamp is connected to the battery via the ignition switch. Since the B+ terminal is hard-wired to the battery, and since both the D+ and B+ diodes are fed from the same set of windings in the alternator, no voltage difference can exist between these two points. The warning lamp goes out.
The voltage regulator "watches" the voltage at the D+ point, which should be the same as that applied to the battery. It now changes the short between the D+ and DF terminals into a variable resistance. This effectively controls the field current (whose source is now the output from the D+ terminal, and not the charge warning lamp) and thus regulates the output voltage of the alternator.
Fault conditions: When something happens to the charging system that causes it's output to be insufficient, the result is almost always a net voltage difference across the charge warning lamp, causing it to light. For example: Suppose an output (B+) diode opens. The efficiency of the main output is now considerably reduced. The voltage regulator does not know this, however, because it is looking at the D+ point. So, the B+ output is now lower than the D+ point and the warning lamp lights. Let's say that one of the D+ diodes failed: The D+ output is now reduced considerably. This means that the voltage regulator will have difficulty in maintaining sufficient field current for normal output. The field regulating resistance is low or short (between D+ and DF terminals) and the resulting load on the crippled D+ system drops it's voltage well below the battery voltage. Therefore, there is a net voltage difference across the charge warning lamp and it lights.
The bottom line is that in order for your light to light, you must have a net imbalance in the outputs of the D+ and B+ sections of the alternator (or between the D+ output and the battery voltage, which amounts to the same thing).

________________________________________________________________________________


To trouble-shoot the problem, you need to check the various sections independently. Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. This is the maximum field current situation, and should result in maximum output of the alternator. Note that this checks the B+ diodes, the alternator windings, and the common diodes. It does NOT check the D+ diodes.
To check the D+ portion of the system, it is necessary to find out if the D+ output can produce enough current to drive the alternator to full output. To do this, short the D+ and DF terminals on the relay board. This will provide the maximum field current to the alternator that the alternator ITSELF can supply (not the battery, as in the earlier check) and so checks the remainder of the circuitry. If this test puts the light out, then the alternator is good, and the trouble is elsewhere. If it doesn't, then the alternator is almost certainly bad, with one other possibility:
In the Bosch system, the size of the charge warning lamp bulb is critical. Too low a wattage bulb will not supply enough field current for "bootstrap" operation to be reliable. The Bosch book that I have states that the lamps must be at least 2 watts for 12 volt systems. If you have replaced your charge warning lamp recently, then too small a lamp may be your culprit.
McMark
Damn!!! That’s a fantastic post. drooley.gif
bulitt
Yes, you must excite the Alternator to wake it up. A bulb, resistor or gauge may be used.
Edward Blume
I had my stock Bosch alternator professionally rebuilt for about $250 in Livermore CA. Dean's. Looks pretty too.
Mikey914
QUOTE(bulitt @ Apr 19 2018, 03:58 PM) *

Yes, you must excite the Alternator to wake it up. A bulb, resistor or gauge may be used.

This is why you can't place a LED in the dash warning light. It inhibits the current to create the field as it is a diode.
jcd914
I don't recall the years but there was a TSB for 911's with certain alternators, that specified installation of a resistor in parallel to the charge indication lamp to boost the current flow thru the alternator for excitation.

We had an alternator/starter shop locally that we used, to avoided any of the rebuilt units available. They turned out a better product that any of out parts suppliers rebuilt units but it took a few days to get them done.
They may still be around I don't know.

Jim
Olympic 914


On Thursday took the alternator to the local FLAPS and had it tested , they said it had a fault but it passed 3 of 4 tests. still no good. so I ordered another alternator and took the bad one to a reputable local auto / truck electrical shop planning to have it rebuilt and keep as a spare... well they tested it and it and said it was good ??? confused24.gif and all my regulators tested good also.

Reinstalled it and it worked for two seconds, count .. one thousand one, one thousand two. before the alt light came on again.... mad.gif So I figured I was out of luck for Hershey. No sense going if I can't take the car.

At 10:15 on Friday morning the Flaps called and said the new alternator came in.so I hurried down to pick it up, Installed it, I had a working charging system now, and after a quick ride around the block, headed off to Hershey.

Where I picked up ANOTHER regulator. this one a Bosch solid state.

So 450 miles later everything is working fine.... Finally...

I guess the alternator was the problem all along but intermittently working, Now I have a bunch of spare regulators and a new Bowlsby wiring harness.

Thanks for your help and suggestions.

Tom



Spoke
beerchug.gif
GregAmy
That post #15 is a gem...

Camping onto this one for a slightly different problem: GEN light comes on strong with key on, engine not running, But then the GEN light glows very soft at idle, and then comes on stronger as RPMs build. Battery is getting ~13.5 volts when running.

QUOTE
Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. This is the maximum field current situation, and should result in maximum output of the alternator.

Check. I get around 15.5V at idle and up to 17+ as I rev it up.

QUOTE
To check the D+ portion of the system, it is necessary to find out if the D+ output can produce enough current to drive the alternator to full output. To do this, short the D+ and DF terminals on the relay board. This will provide the maximum field current to the alternator that the alternator ITSELF can supply

Check. Same as above, 15+ V at idle and 17+ as I rev it up.

Problem is, I can't check to see if it extiguishes the GEN light, because my GEN light is not on with the voltage regulator removed. It'll only come on with the regulator installed. This makes sense, because looking at the wiring diagram the ground side of the GEN light is through the voltage regulator; it's blocked by diodes at the alternator from grounding.

Does everyone else's GEN light come on with key on and engine off when the VR is removed?

I did some further checks. Pulled the combo gauge out and measured voltage at the GEN light housing. With the engine off I'm getting 0V across the terminals, but with the engine running I'm getting ~2V at idle with the blue (D+) wire hotter than the red (system) voltage wire, rising to nearly 4V at revs. Measured to ground, I'm getting system (~13.5V) voltage from the S9 fuse and ~15.5V at idle and ~17.5V (max alternator output) at the blue D+.

That would certainly explain the glowing bulb.

So here's the key question: what is supposed to be at D+? I'm guessing the same as system. B+ is being regulated, so the rest of the car is getting the proper voltage, it's just the D+ wire that's too hot. Unfortunately, I don't know enough about these systems to understand why that could happen.

Since the rest of the car is not overcharging it seems safe to drive, and it'll still glow bright if I fail the alternator, but I'd prefer to not ignore it.

I REALLY don't want to replace the alternator in this thing...Thoughts appreciated.

Greg

Edit: an added data point. I swapped out the Hella solid state VR for a resgular Bosch VR of unknown provenance. Now I'm getting 13.5 on the D+ side and 12.2 on the B+ side. I might just buy a new VR from a local FLAPS and see if that resolves it.
Spoke
QUOTE(GregAmy @ May 13 2018, 03:22 PM) *

Does everyone else's GEN light come on with key on and engine off when the VR is removed?

Yes, the light is on with key on and engine not running and off with VR removed.

QUOTE

Measured to ground, I'm getting system (~13.5V) voltage from the S9 fuse and ~15.5V at idle and ~17.5V (max alternator output) at the blue D+.

That would certainly explain the glowing bulb.

I'm not sure I follow your measurements. What are the 2 measurements at S9 and D+ both to ground at the same condition with the VR installed? At idle and 2k RPM. The difference between the voltage at S9 and D+ is the voltage across the GEN light.

These 2 voltage come from the 2 steering diode pins on the alternator which derive voltage from the same stator windings. They should always be the same during operation. This could point to alternator diode issue although I wouldn't replace the alternator unless sure it's not the VR. It would be convenient to swap the VR for a known good one before buying a new VR.

QUOTE

So here's the key question: what is supposed to be at D+?


D+ doesn't matter in this case. D+ is the voltage across the armature to provide field current for the armature coil. It will vary with load. The VR controls this.

QUOTE

Since the rest of the car is not overcharging it seems safe to drive, and it'll still glow bright if I fail the alternator, but I'd prefer to not ignore it.


Agreed it should be ok as long as the battery voltage stays above 13V and below 15V.
GregAmy
QUOTE(Spoke @ May 13 2018, 04:20 PM) *
Yes, the light is on with key on and engine not running and off with VR removed.

How? Look at the wiring diagram: if you remove the voltage regulator then to what circuit will the GEN lamp ground? The diodes in the alternator should stop it from being grounded there, leaving only the circuits in the voltage regulator...so, to the wiring diagram, the GEN light should not be on with the VR removed and the key on.

Have you observed it that way yourself? If not, give it a try.

QUOTE
I'm not sure I follow your measurements. What are the 2 measurements at S9 and D+ both to ground at the same condition with the VR installed?


Exactly as I wrote above: "Measured to ground, I'm getting system (~13.5V) voltage from the S9 fuse and ~15.5V at idle and ~17.5V (max alternator output) at the blue D+."

Direct to battery using the same ground is within 0.2V of S9, as measured on the S9 side of the GEN light housing.
QUOTE
These 2 voltage come from the 2 steering diode pins on the alternator which derive voltage from the same stator windings. They should always be the same during operation.

"Should".

Ain't.
Spoke
QUOTE(GregAmy @ May 13 2018, 05:45 PM) *

QUOTE(Spoke @ May 13 2018, 04:20 PM) *
Yes, the light is on with key on and engine not running and off with VR removed.

How? Look at the wiring diagram: if you remove the voltage regulator then to what circuit will the GEN lamp ground? The diodes in the alternator should stop it from being grounded there, leaving only the circuits in the voltage regulator...so, to the wiring diagram, the GEN light should not be on with the VR removed and the key on.

Have you observed it that way yourself? If not, give it a try.

QUOTE
I'm not sure I follow your measurements. What are the 2 measurements at S9 and D+ both to ground at the same condition with the VR installed?


Exactly as I wrote above: "Measured to ground, I'm getting system (~13.5V) voltage from the S9 fuse and ~15.5V at idle and ~17.5V (max alternator output) at the blue D+."

Direct to battery using the same ground is within 0.2V of S9, as measured on the S9 side of the GEN light housing.
QUOTE
These 2 voltage come from the 2 steering diode pins on the alternator which derive voltage from the same stator windings. They should always be the same during operation.

"Should".

Ain't.


I re-read my post and I had a few things wrong.

= With VR removed and engine not running, S9 is battery voltage (12.6V). The load looking into the D+ wire is infinite since the VR is the only load. and with the VR removed, electrically you only see the cathodes of the 3 alternator diodes. The GEN light doesn't light since current cannot flow into the cathodes of the 3 diodes.

= I said the voltage at D+ doesn't matter. I had confused D+ with DF. D+ should be exactly the same as the battery voltage. DF is variable with load and is controlled by the VR.

= About the measurements, here's what I think you've measured with the VR INSTALLED:

At idle:
V(S9) V(D+)
13.5V 15.5V

At elevated RPM
V(S9) V(D+)
13.5V 17.5V

Or are these numbers with VR REMOVED and D+ directly connected to DF?

euro911
Jerry, what's the best method for bench testing our alternators? (out of the car) ... I have several 'unknown condition' units I'd like to check out.

I took one to Autozone several years ago and they said their machine didn't have the correct connector to test a type-4 alternator screwy.gif
GregAmy
QUOTE(Spoke @ May 13 2018, 07:30 PM) *

= About the measurements, here's what I think you've measured with the VR INSTALLED:

At idle:
V(S9) V(D+)
13.5V 15.5V

At elevated RPM
V(S9) V(D+)
13.5V 17.5V

Or are these numbers with VR REMOVED and D+ directly connected to DF?

I am going to check these again tonight. But the S9 and D+ measurements at the GEN bulb housing were with VR installed; the only VR-out checks I did were for the tests in post #15, where I connected B to D+ and jumped D+ to DF; both tests showed max alternator output, ~17.5 volts.

I wish I knew alternators better (that's some serious magic, like CV joints and rotary engines) but it makes no sense that I'm seeing system/battery voltage on S9 but what seems to be max alternater output on D+.

More data tonight.
GregAmy
QUOTE(Spoke @ May 13 2018, 07:30 PM) *

= About the measurements, here's what I think you've measured with the VR INSTALLED:

Prior to start up
12.15V at the battery.

Voltage between from combo gauge housing (my ground inside) to battery 12.15

Key on, removed bulb:
11.83V between combo housing and red/white wire
0V between combo and blue wire

So my S9 circuit has a dirty connection somewhere, I'm losing 1/2V to the combo gauge.

Bulb back in, start car:
13.35V battery to combo gauge housing

13.32V between combo housing and red/white wire @ idle
~15.5v between combo housing and blue wire @ idle
Bulb glowing slightly

13.51V between combo housing and red/white wire @ revved
17.34V observed between combo housing and blue wire @ revved
Bulb glowing brighter, but not as bright as key on engine off.

Reminder: when I tested Battery to D+ and DF to D+ I got max alternator voltage both times.

So why is D+ showing max alternator output voltage when it's supposed to be the same as B+?

I'm'a gonna hit a FLAPS for a new voltage regulator, not really hopeful but fingers crossed.
GregAmy
Aaaaand a new voltage regulator...

...didn't resolve it. Same problem. Wish I understood alternators better so I could understand the problem, but oh well. And I get to replace the alternator pigtail with a new one.

At least now I have a spare VR. Odd one too, from Echlin, remote mounts.

Who makes our preferred alternator so I won't have to do that job again? I've done it once before and I remember it was a fiddly job.

Dammit.


Click to view attachment
Spoke
Bummer. I didn't think the VR was at fault but it is an easy swap to find out.

Are all the ground straps (Battery to chassis; chassis to transmission) clean and tight?
GregAmy
Yep. All grounds and battery cables replaced by me a couple years ago.

Have not replaced the alternator pigtail though. I wonder if that's accessible with the alternator in the car?
dangrouche
QUOTE(GregAmy @ May 16 2018, 05:42 AM) *

Yep. All grounds and battery cables replaced by me a couple years ago.

Have not replaced the alternator pigtail though. I wonder if that's accessible with the alternator in the car?

the pigtail at the alternator end needs the alternator removed, and the metal cover shield removed as well. sad.gif

HERE IS METHOD TO TROUBLESHOOT THE INSTALLED ALTERNATOR:
I did have a complete functional alternator assembly(alternator with the pigtail connected). I attached an alligator clip to the "extra alternator" body and grounded it to the car. I also did the same by connecting the positive terminal of the the external alternator to the car battery terminal. I plugged in the pigtail of the extra alternator onto the relay board. I switched the ignition key to the "on" position. I looked at the idiot light to see whether it glowed or not. (It did not glow with the installed alternator. ) The idiot light DID glow with the extra alternator, which meant installed alternator was failed (diode or brushes).

At least this way, I did not have to go to the trouble of pulling and testing the installed alternator. In the end, I rebuilt the installed alternator for $15 with a pair of alternator brushes from RockAuto.
GregAmy
QUOTE(dangrouche @ May 17 2018, 01:27 PM) *
the pigtail at the alternator end needs the alternator removed, and the metal cover shield removed as well. sad.gif

Yeah. I had the race car on the lift so looked it over last night and it needs to be removed.

I've got a spare alternator on the bench, one removed some time ago, so I'm looking around to see if I can find someone to rebuild it. I'm in no rush; as noted before, best I can tell the only thing connected to the 17V on the D+ side is the GEN lamp, and with system at 13.5V it won't hurt anything for now while I get a replacement lined up.
dangrouche
https://www.aspwholesale.com/index.php

here is a website that sells the bearings and brushes parts if you are up to rebuilding it yourself
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