Another Brake Warning Light Challenge

[jhmol]

I have a brake warning light that is on that just won't stay out. Someone must know what is going on....
The e-brake switch has been adjusted and works as desired.
The brakes have been checked on a test machine. Not sure of the units, but are strong and even 320 front and 260 rear.
The brake pedal is firm with no leaks detected.
Both brake switches were just replaced and brake fluid replaced.
The brake warning light goes out with a battery reset, but comes back on and stays on with light use of the brakes.
So... replacing the master cylinder appears to be next, but doesn't make sense when the brakes are strong and even. Anyone? This is driving me nuts... sure a weak car pun.

John
82 911SC about 90,000 miles

[Darkly-Noon]

You didn't mention if the brake lights were working properly. I had the exact same symptoms on mine recently and it was just the bulb. Note that the bulb only goes in one way - the little side protrusions on the base are at different spots.

[joe payne]

Mine did that when I tried to use LED bulbs.

[tazzieman]

Mine did that ; I replaced the pressure switches also and it made no difference. Brakes were fine all along. I cleaned up all the rear connections and replaced bulbs. The warning light stayed on but one day it just seemed to go off and work normally from there on in.
If you've checked the lights/housings/connectors I'd just continue to drive it , keep an eye on the fluid level - and one day the warning light may just decide to behave!

[jhmol]

Thanks DN, Joe, and tazzleman,
The brake lights are a possibility... In order to pass inspection, I had to "bump" my right rear turn signal light. The brake light, left or right, could be loose or installed wrong. I like tazzleman's solution (wait until it fixes itself)...but that red light in the cockpit is difficult for me to ignore. Yes, I'm that way.
So... my plan of attack is to check my bulbs and sockets.. clean them even if they are clean... better than replacing a working master cylinder. Thanks for chiming in.

[86 911 Targa]

Do you have the pad wear sensors?

[SCadaddle]

Do us a favor and report back once you fix it. In the meantime I'll let the brake warning light in the dash of my 82 SC shine on......

[Jonny H]

You possibly have the wrong brake light switches fitted, happened to me, see here

Resetting the Brake warning light - Brakes - Impact Bumpers

[RDM]

Originally Posted by 86 911 Targa

Do you have the pad wear sensors?

Not on SCs.

Originally Posted by Jonny H

You possibly have the wrong brake light switches fitted, happened to me, see here

Resetting the Brake warning light - Brakes - Impact Bumpers

Very interesting thread, well described and illustrated. I'd check this.

[will hung]

Mine had similar symptoms for about 2 years. Drove me crazy. I never suspected my brake lights were the culprit because I passed to state inspections at that time.

Then one day I took my car for a drive in the evening. The brake warning light had come on again, so when I got back, I left the car running and was checking the voltages at my battery in case my new alternator was not charging properly (which I read can cause the issue).

While testing, my neighbor walked over and told me that my brake light wasn't working. I went over, pushed the brake pedal in, and they both worked. He told me that he watched me back out of my driveway and that my driver side brake light wasn't working. I then turned my headlights on and pushed the brake pedal, then it didn't work.

Many weeks pouring over wiring diagrams, many weeks refurbing tail light housings, and many dollars spent later, I found that I had a break in the wiring at the plug in the engine compartment.

Soldered in a new plug and no more warning lights.

[targa80]

In my case I had a mild case of spongy pedal, it took awhile for the pedal to sink while pressing hard on it. Turns out it was an internal leak in the brake master cylinder. Replaced it and problem solved

[GH85Carrera]

The sockets for the bulb are not a real robust design. I had to take mine off of the car and carefully clean all the dirt and corrosion off of them. A little buffing and then dielectric grease. Problem fixed.

[wwest]

That is generally a sign that the battery is being over charged, watch out for tach jumping next, and rev limiter lockup upcoming next.

Check the alternator output voltage at/in the engine compartment AND at the battery posts at 2000 RPM and low electrical loading.

[RDM]

Originally Posted by wwest

That is generally a sign that the battery is being over charged, watch out for tach jumping next, and rev limiter lockup upcoming next.

Check the alternator output voltage at/in the engine compartment AND at the battery posts at 2000 RPM and low electrical loading.

Interesting. Alternator has been replaced in the last year, and I know he keeps a voltage meter nearby. Even so, it's worth a look.

John is camping with his scouts, so let me see what I can add. The switch replacement was done in my garage, so I still have the old parts. I In the spirit of Jonny H's link, I checked the switches we took out. I believe the correct poles are connected.



Here's the box for the new switches.



As I think about it, since the behavior of the light is the same now as it was before, it's doubtful that the switches are wrong. Stranger things have happened, though.

We used a plastic syringe to try to fill the switches with fluid before attaching them. The syringe would deliver fluid to the hole, but not into the hole. Is there a better way to ensure the switch is bled?

[SCadaddle]

Originally Posted by SCadaddle

Do us a favor and report back once you fix it. In the meantime I'll let the brake warning light in the dash of my 82 SC shine on......

As a follow up, I just went out and using a narrow piece of Scotchbright cleaned my brake light bulbs and housings. My problem is resolved for now. No red warning light!

[wwest]

To the best of my knowledge the red brake indicator has no relation to the brake lights or brake light switch. Lights only to indicate e-brake is engaged or low fluid, other than some type of failure/fault that is.

[wwest]

Originally Posted by tazzieman

Mine did that ; I replaced the pressure switches also and it made no difference. Brakes were fine all along. I cleaned up all the rear connections and replaced bulbs. The warning light stayed on but one day it just seemed to go off and work normally from there on in.
If you've checked the lights/housings/connectors I'd just continue to drive it , keep an eye on the fluid level - and one day the warning light may just decide to behave!

"..one day.." shortly after you replaced the alternator/regulator/battery?

[jhmol]

Okay... The Pelican heads may have done it again. The left brake light is out. I checked that immediately after reseting the brake light with the battery disconnected and hitting the brakes once hard in the garage with the light coming on immediately. I'm not currently in the right condition to start minor surgery on the car (Dru did say I had camped all weekend with the scouts) so I will wait a day, see if I have a replacement bulb or get out my multimeter and see what's going on.
I know I'm not there yet...but it would have been pretty sad to replace the master brake cylinder for want of a stupid light bulb.
Thanks all. I will follow up once said bulb has been replaced/tested.
John

PS. I am certain there is a smarter way of checking the brake light solo than using a field hockey stick propped between the brake pedal and the drivers seat pushed forward by a plastic wiffle ball bat... but I'm just guessing.

[wwest]

PS is correct.

Can EVERYONE chime in.... who knows, says, different??


The brake warning light is on ONLY for e-brake or low brake fluid!!!

Or in your case possibly an alternator over voltage indicator.

[tazzieman]

Originally Posted by wwest

"..one day.." shortly after you replaced the alternator/regulator/battery?

No , just one day.