Generator Light, Is On Options

[Spoke]

New alternator, battery, and voltage regulator. Still on... (IMG:style_emoticons/default/headbang.gif)

So all the electrical components are new and the GEN light is still on?

As mentioned before, if all components are new and the GEN light is still on, then likely you have a wiring issue. The only way to track this down is to measure the system in different points to see if you have the correct voltages.

See the 914 charging system diagram below. It may look complicated but it is quite simple; only 4 components: Alternator, Voltage Regulator, Battery, and GEN light.

Short version of what's going on starting with the alternator. The flux capacitor looking thing in the middle is the STATOR which are the stationary windings and produces a 3-phase AC voltage when running. Above it is the ARMATURE which is a voltage-controlled magnet and is the spinning part. There are 3 banks of diodes, one for each of the 3-phase STATOR windings.

The bottom right bank of diodes is connected to ground and is the return path for current. The top right bank charges the battery. Heavy currents can flow in this path. The top left bank drives the voltage regulator and the left side of the GEN light.

The voltage at alternator pins D+ (top left diode bank) and B+ (top right diode bank) are the same voltage (12.6V to 14V) during operation. When B+ equals D+, the GEN light is out.

Follow the D+ wire from the alternator to the left side of the GEN light. Now follow the B+ wire from the alternator through Fuse 9 to the right side of the GEN light.

In operation, D+ and B+ are the same voltage and the GEN light is OFF. Your GEN light is ON. Do this test:
1) with ignition off, pull the gauge out with the GEN light.
2) Start the car and rev the engine a few times to bootstrap the alternator.
3) Measure the voltage (to ground) on both sides of the GEN light; they should be the same voltage.
4) Write down the voltages and report back on this thread.
5) Depends on what you find in 4). (IMG:style_emoticons/default/beerchug.gif)

[EdwardBlume]

Thanks for the great information Spoke! I'll track it down.
In the meantime, I also had my generator rebuilt by Deans in Livermore CA. Really great work! Super guy too!

[porschetub]

What did they find wrong with it ?

[EdwardBlume]

It tested good but when he opened it up, the diodes and brushes were nearly spent. All new everything, it's as good as new. Cost me about $200.

[EdwardBlume]

I got the new alternator installed. Fully charged new battery. New VR.

Light is still on...

[4) Write down the voltages and report back on this thread.]

One side is 12.0 ish, the other is 12.7 ish. Both at idle.

[EdwardBlume]

I re-read your instructions to test it to ground.

I got a floating 11.7-12.5 on the red / white side, and 0.05 on the other side. This time ground (to the shifter).

[IronHillRestorations]

$200 is a lot. The list for a Bosch reman at my local NAPA was about $145, and this is reman'd by Bosch with a 24 month warranty.

[Spoke]

Rob,

Copying my PM to you with additional info:

Since you've changed the alternator, VR, and battery, I have questions about the operation.

Do you measure those numbers right after starting the car or after a bit of driving? Does the light go out or on dimly?

With all new components, it may be some of the wiring at issue. Don't think it's a short. May be a corroded or oxidized connection somewhere.

Does the light go out when the engine speed is elevated to 2k RPM or above?

On the wire going from the alternator to the VR, measure the voltage on the RED wire to chassis and BROWN wire to chassis. The RED wire is the wire going to the GEN light. Just checking if there's some voltage drop from the VR to the GEN light. The BROWN wire is alternator ground. Just checking to make sure the engine/alternator is grounded.

What voltage do you measure on the battery? Measure this from battery post to chassis ground.

When the engine speed is elevated to 2k RPM, what do you measure on the battery?

What is the condition of the transmission ground strap? Have you cleaned/checked the connections?


What is the condition of the battery ground strap? Have you cleaned/checked the connections?

Any bit of oxidation or corroded wires/connections can cause huge problems for the charging system.

[Spoke]

I got the new alternator installed. Fully charged new battery. New VR.

Light is still on...

[4) Write down the voltages and report back on this thread.]

One side is 12.0 ish, the other is 12.7 ish. Both at idle.

I got a floating 11.7-12.5 on the red / white side, and 0.05 on the other side. This time ground (to the shifter).

Which measurement is correct? The second one with 12.5 and 0.05? If so, the 0.05 is not right.

The RED/WHITE wire comes from the battery through fuse F9. The other wire should be BLUE (according to my Haynes manual) coming from the VR. It's voltage should match the battery voltage.

[EdwardBlume]

$200 is a lot. The list for a Bosch reman at my local NAPA was about $145, and this is reman'd by Bosch with a 24 month warranty.

I get it. This was custom rebuilding by a guy in Livermore. Worth the connection.

[EdwardBlume]

Rob,

Copying my PM to you with additional info:

Since you've changed the alternator, VR, and battery, I have questions about the operation.

Do you measure those numbers right after starting the car or after a bit of driving? Does the light go out or on dimly?

A: At startup, a few revs and measured at idle. The light never goes out. Months ago it came on while driving. Went off for a little bit on the way home, and then stayed on. Been on ever since.

With all new components, it may be some of the wiring at issue. Don't think it's a short. May be a corroded or oxidized connection somewhere.

A: From what I can tell, the blue wire joins the harness off the relay board. So you may be right about corrosion or the board perhaps?


Does the light go out when the engine speed is elevated to 2k RPM or above?

A: No

On the wire going from the alternator to the VR, measure the voltage on the RED wire to chassis and BROWN wire to chassis. The RED wire is the wire going to the GEN light. Just checking if there's some voltage drop from the VR to the GEN light. The BROWN wire is alternator ground. Just checking to make sure the engine/alternator is grounded.

A: Its a new harness.

What voltage do you measure on the battery? Measure this from battery post to chassis ground.

A: Will check again tomorrow.

When the engine speed is elevated to 2k RPM, what do you measure on the battery?

A: Volt gauge moves up on revs so the alt is working. I can test that tomorrow.

What is the condition of the transmission ground strap? Have you cleaned/checked the connections?

A: Visually. I'll pull it tomorrow.


What is the condition of the battery ground strap? Have you cleaned/checked the connections?

A: Visually. Will pull it tomorrow.

Any bit of oxidation or corroded wires/connections can cause huge problems for the charging system.

A: I installed a new harness so I know everything is working up to the relay board.

Thanks Spoke. We'll get this! I appreciate your help with Dad's car.

[EdwardBlume]

I got the new alternator installed. Fully charged new battery. New VR.

Light is still on...

[4) Write down the voltages and report back on this thread.]

One side is 12.0 ish, the other is 12.7 ish. Both at idle.

I got a floating 11.7-12.5 on the red / white side, and 0.05 on the other side. This time ground (to the shifter).

Which measurement is correct? The second one with 12.5 and 0.05? If so, the 0.05 is not right.

The RED/WHITE wire comes from the battery through fuse F9. The other wire should be BLUE (according to my Haynes manual) coming from the VR. It's voltage should match the battery voltage.

The first reading I didn't ground. I connected the inputs so I was getting the current from the red / white side.

The second readings I grounded to the shifter.