Master cylinder switch and reset. Options

[Keith914]

I have installed a new 19mm master cylinder that came with a single switch. My '72 harness to this switch has two wires each with a female "push on" connector, but the new brake master cylinder switch has only one male connector on it, next to the reset (?) switch. Two questions: 1) do I need to find a two connector switch, and 2) how do you reset the switch? I pushed the little black button into the switch and I think a felt it go in with a slight "snap".

[BeatNavy]

The old MC switches grounded with the brown wire on your wiring harness. The new switch grounds through the MC itself. Just tape up the brown wire on your harness - you don't need it with the new MC.

That switch you pushed should be the reset switch.

[Keith914]

Thanks for your prompt helpful response. I will report back.

[Keith914]

Thanks for your prompt helpful response. I will report back.

I selected the brown ground wire and taped it off carefully, then attached the brown with white stripe wire to the single male fitting on the master cylinder switch. Unfortunately when I turn the ignition on again the brake light continues to flash on and off at about the frequency of the turn signals, and when I switch the right or left turn signals on while the brake light is flashing, the right signal flashes weakly while the left turn signal is on, and visa versa? I previously inspected the hand brake switch adjustment and condition of the sensor wire -- all looks OK.

[era vulgaris]

Are you talking about the blinking light that's part of your fuel/combo gauge? That's for the handbrake. Release the handbrake and it should stop blinking. I think the switch on the MC is for the red brake failure warning light above the HVAC controls.

[Larmo63]

(IMG:style_emoticons/default/agree.gif)

[Keith914]

The old MC switches grounded with the brown wire on your wiring harness. The new switch grounds through the MC itself. Just tape up the brown wire on your harness - you don't need it with the new MC.

That switch you pushed should be the reset switch.

I have completed your suggestion to properly connect the harness to the master cylinder switch but no change in problem symptom.

In my search I pulled the gas/brake warning light gauge out and cleaned up some of the harness gauge connections. I found a strange (to me) connection between the generator light and the brake warning lights, about 4 inches long beginning and ending with about 1 inch of typical harness size insulated copper wire, each with a female connection to the gauge lights mentioned above, but about 2 inches in the middle of a length of strong bare silver wire shrink wrapped in shiny black plastic about 1/8" diameter encased in a hard black plastic tube slipped over the shrink wrap. This wire is soldered at each end to the two 1" lengths of typical harness wire mentioned above. One of the soldered connections was broken. I repaired (solder) it, but it has not corrected the fault I am attempting to fix?

I am about to remove the driver's seat to access and check the operation of the handbrake switch.

[Dave_Darling]

That thing you describe may be a diode to keep the power from going "backwards" through the system.

The blinking light in the combo gauge will blink when the key is on and EITHER the handbrake handle is up and not pressing on the handbrake handle switch, OR the master cylinder switch is closed.

If the wire going to either of those switches is shorted to ground, the light will also flash.

--DD

[BeatNavy]

Stupid question, but does the brake system need to be filled / bled before you can actually reset the switch at the MC (and have it stay)?

[Keith914]

Not a stupid question. Along with replacing the master cylinder, I replaced the front calipers with the recommended BMW 320 I calipers. I have since bled the rear and front calipers thoroughly with a pedal finally stopping about half way down, and which I expect to improve once the new pads in front have "set in".

[Keith914]

That thing you describe may be a diode to keep the power from going "backwards" through the system.

The blinking light in the combo gauge will blink when the key is on and EITHER the handbrake handle is up and not pressing on the handbrake handle switch, OR the master cylinder switch is closed.

If the wire going to either of those switches is shorted to ground, the light will also flash.

--DD

Thanks Dave. I will tackle this again tomorrow checking the wires for shorting.

[Keith914]

Stupid question, but does the brake system need to be filled / bled before you can actually reset the switch at the MC (and have it stay)?

Thought about it more last night. With my ohmmeter, I checked for continuity in the master cylinder switch. Found that the single connector (male) is grounded, this after checking that the small rubber sleeved reset button is firmly in the depressed position, I can't press it in further with my finger. Is this new switch (came with the new 19mm master cylinder) faulty?

[Keith914]

The old MC switches grounded with the brown wire on your wiring harness. The new switch grounds through the MC itself. Just tape up the brown wire on your harness - you don't need it with the new MC.

That switch you pushed should be the reset switch.

Have now thoroughly checked the emergency brake switch condition and setting -- all OK. What should I try next?

[BeatNavy]

Stupid question, but does the brake system need to be filled / bled before you can actually reset the switch at the MC (and have it stay)?

Thought about it more last night. With my ohmmeter, I checked for continuity in the master cylinder switch. Found that the single connector (male) is grounded, this after checking that the small rubber sleeved reset button is firmly in the depressed position, I can't press it in further with my finger. Is this new switch (came with the new 19mm master cylinder) faulty?

I suppose the switch could be faulty at this point. I have a brand new ATE 19mm MC on the bench, and for sanity purposes I checked continuity between that male connector and all over the MC. Nada - no continuity, and the switch is pressed in.

So I assume yours should not be grounding. It sounds like that switch is not resetting properly or the switch is faulty. I believe you can buy just the switch, but what a pain, eh?

[Keith914]

Yes a PITA! Any suggestions where I can buy one?
Further, also just tested my refurbished fuel delivery system with Tangerine SS tunnel pipe. All buttoned up, switched the ignition on, hear pump running, then smell gas. New in line (with T connection) fuel pressure gauge spewing gas, WTF. Removed the gauge, opened it up. Sure enough the solder connection expanding copper tube to brass base leaking!! Need a different brand 15p.s.i. gauge (carbs).

[BeatNavy]

Yes a PITA! Any suggestions where I can buy one?
Further, also just tested my refurbished fuel delivery system with Tangerine SS tunnel pipe. All buttoned up, switched the ignition on, hear pump running, then smell gas. New in line (with T connection) fuel pressure gauge spewing gas, WTF. Removed the gauge, opened it up. Sure enough the solder connection expanding copper tube to brass base leaking!! Need a different brand 15p.s.i. gauge (carbs).

One step forward, two steps backward, eh? Hang in there.

This is the only switch I saw, but I'm not 100% sure this is what you need for your application: https://europortparts.com/sku/90161311500.1...CFcYfhgodpSwN9g

May want to ask Eric at PMB.

[Dave_Darling]

Find what is grounded. Is the MC switch providing the ground? Is the handbrake switch providing it? Is something else?

--DD

[Keith914]

Yes a PITA! Any suggestions where I can buy one?
Further, also just tested my refurbished fuel delivery system with Tangerine SS tunnel pipe. All buttoned up, switched the ignition on, hear pump running, then smell gas. New in line (with T connection) fuel pressure gauge spewing gas, WTF. Removed the gauge, opened it up. Sure enough the solder connection expanding copper tube to brass base leaking!! Need a different brand 15p.s.i. gauge (carbs).

One step forward, two steps backward, eh? Hang in there.

This is the only switch I saw, but I'm not 100% sure this is what you need for your application: https://europortparts.com/sku/90161311500.1...CFcYfhgodpSwN9g

May want to ask Eric at PMB.

My apology, I now find the MC switch is not grounded -- appears to be OK. Brake warning light is still flashing when turning on ignition. Inspected emergency brake switch which is in good order. So left with tracing wiring (laborious and difficult) or the turn signal relay is faulty. Will test with a fellow 914Worlder's relay along with tracing the wiring from the emergency brake and master cylinder to the fuse panel.

[BeatNavy]

That's progress, I think. I would rather trace the wiring and try to find the offending ground than deal with a faulty MC or MC switch. It's really only two wires, and one of them is inadvertently grounded.

How did you check the E-brake switch? I would pull that thing out, inspect it, and then check continuity from that wire to ground. That little switch gets a little abused due to its use/location and may have failed.

[worn]

Yes a PITA! Any suggestions where I can buy one?
Further, also just tested my refurbished fuel delivery system with Tangerine SS tunnel pipe. All buttoned up, switched the ignition on, hear pump running, then smell gas. New in line (with T connection) fuel pressure gauge spewing gas, WTF. Removed the gauge, opened it up. Sure enough the solder connection expanding copper tube to brass base leaking!! Need a different brand 15p.s.i. gauge (carbs).

One step forward, two steps backward, eh? Hang in there.

This is the only switch I saw, but I'm not 100% sure this is what you need for your application: https://europortparts.com/sku/90161311500.1...CFcYfhgodpSwN9g

May want to ask Eric at PMB.

My apology, I now find the MC switch is not grounded -- appears to be OK. Brake warning light is still flashing when turning on ignition. Inspected emergency brake switch which is in good order. So left with tracing wiring (laborious and difficult) or the turn signal relay is faulty. Will test with a fellow 914Worlder's relay along with tracing the wiring from the emergency brake and master cylinder to the fuse panel.

I got eye strain tracing different wires on the several different charts available.

There is a thin line between clever and stupid. And Porsche was skating on that line. The warning light crams a lot in. First, the light tests itself through a diode when you turn the switch on until start up. Second there is the hand brake switch. Third is the wire to the shuttle in the MC. Finally on some models there is a wire to the seat belt system. If the buzzer has been disabled by normal routes that will not be a problem. I found on my '72 a taped-off wire to go to a float to tell you when the brake fluid is low. As far as I know I am the only person to have it installed cause they decided not to use it in production.

Uber-efficient. No wasted wires, and the good news is they are all brown with white and they all will activate the light and flasher if they are grounded. So - you can assume one of them is grounded.