on-air

Hi all

I have an 1981 928 with 40,500 original miles, car is in near museum like original condition. Recently I've been having problems with not having brake lights. Here's the symptoms; start the car, all warning lights appear like normal. Step on the brake to clear the stop lamp check warning, and about half the time the Stop Lamp warning does not go off as it should when I step on the brake pedal, and I notice I also don't have brake lights. Sometimes it works as it should and I have brake lights. Sometimes I will step on the brake and the Stop Lamp warning goes off and I have brake lights initially, but then after a few more repeat steps on the brakes, no brake lights (and no Stop Lamp warning again), and then a few steps later brake lights work again.

All other electrical items (fog lights, head lights, blinkers, fan etc) work fine.

here's what I've done so far:

-replaced the brake light bulbs with two matched good ones, checked all other tail light and side marker bulbs-all good.

-cleaned all grounds around the car includign the ground on the back right quarter panel.

-inspected each socket, and cleaned contacts

-both brake pressure switches were replaced a couple years / about 5k miles ago when I was getting a "brake pressure' warning -that's warning hasn't come back since

-replaced brake light fuse

-replaced CWS brain

-replaced battery



so what's next logical step? -- replace LCU? Ignition Switch?



-Kerry
1978 911sc targa
1981 928
1989 951
2002 Boxster

MainePorsche

You've checked/done quite a bit. Didn't see status of wires in the tail light harness mentioned. Anything looked cracked or corroded there ?

on-air

tail light harness wires there look good, nothing suspicious looking

on-air

I should add, yesterday while I had the car parked and ideling, trying to clear the brake light warning, i jiggled the key while steping on the brake, 'voila' brake light came on, but I couldn't consistently replicate that the next time. -- not sure if that is a sign of a bad ignition switch or a red-herring ? -- if it was the ignition switch failing, wouldn't I see other electrical oddities?

MainePorsche

Sorry, but I'm nowhere near my Wiring Diagrams. You've covered a lot, and I'm wondering about the Lamp Control Unit. I had done some work there when I put sidemarker LED's and a third brake light flasher in, and had to disconnect two pins in order not to get a continuous warning. Another will chime in I'm sure.

Add: just saw the post. I would expect other oddities if ignition switch were faulted, but odd things will occur.

GlenL

I'd suspect the brake pressure switches. Not hard or expensive to put in new ones. Get good quality units and not $5 versions. These are common VW parts and are widely made.

on-air

thanks, I too suspected the brake pressure switches, the only thing that I hesitated on there was I replaced them with good quality ones from one of our favorite online Porsche 928 specialists just a couple years / 5k miles ago. But, it sure does sound like a possible problem/solution. Could a bad LCU also cause these symptoms? -- its still an original unit.

GlenL

That only monitors the lights but anything is possible. Do you have an electrical diagram and have you traced the wires to see what's powered with 12V when the pedal is pressed?

Jeff Bowlsby

Would love to see photos of your 1981. My 1981 has 36K miles. Wish I could figure out how to fix the dash cover blisters under the leather, seems like a common issue with th4ese early cars.

Ducman82

on my 81 the stop lamp light likes to come on during hot days.. and mostly , but not always if the road has a small small bump or "jolt". everything has been replaced... makes me insane some times....

The Forgotten On

The light should come on and always stay on while the car is running and only turn off when you step on the brake pedal.

It should then immediately come back on again when you remove pressure from the pedal.

That's how it works in my 81. I also replaced my master cylinder with a new ATE one, but even before that the original switches worked flawlessly with 130K miles on them.

I did have issues with the warning system itself until I replaced the ignition switch which got rid of most of them.

You could try that, they're only ~$100 for the real one and it will give you peace of mind knowing you won't have to worry about it failing any time soon.

Ducman82

the "stop lamp" light should alway come on when you start the car, then it should go off after you hit the brake. thats it. its not not pulse on and off when you hit the brake...

the light should also be able to be cleared with the warning (!) switch. but if you have a real issue it will light back up.

R.Pires

Hi,

I had a similar problem with a rear parking/presence light, with a known good bulb, sometimes working perfectly sometimes was out for a long time without any particular reason and after that it came on again for a long period.
After trying a lot of things without success my electrician found a bad solder inside the lamp control unit! Re-solder it and since then it's been perfect,
just my 2 cents....

Regards

on-air

Thanks everyone
Jeff, here's a few photos of my '81 928. it is a 5 speed manual and came with what Porsche called the 'competition package' for the US market

joejoe

My goodness that is nice looking.