Parking Light Problem

ebrownson · 11-24-2001, 07:31 AM

Hey Guys:

I've had a problem with the left rear parking light/brake light on my 1983 911 SC for some time now. Here are the details:

The left rear parking light/brake light seems to be blowing fuses after a short (no pun intended) period of time. The five amp fuse located in fuse block #4 is also connected to the engine compartment light. When the parking lights are engaged, the left rear parking light burns brightly, brighter than the right side. The bulb is a dual filament kind (standard 1157 bulb) which illuminates both the parking and brake lights. When I turn the lights on, the larger filament (brake) turns on while the smaller filament (parking) does not glow. I removed the grounding wires located behind the light box and in front of the battery and polished them with a dremel tool using a fine abrasive. That did not seem to improve things any.

I also removed the back panel of the light box and checked the wiring. There didn't appear to be any crossed or frayed wires and all connections were nice clean copper with no corrosion.

I am at a loss for what to do next. What is causing this problem? Because it is on one side only, I suspect it is not a problem with my light switch. Am I right? I checked and polished the grounds. Are there any other ground points that I missed? Any other connections that I can check and/or clean?

Nothing like a little Thanksgiving weekend porsche project that can keep me from doing "honey do's". I appreciate any help, suggestions or advise. Hope everyone is having a nice holiday.

Eric
83SC

Doug Zielke · 11-24-2001, 07:54 AM

Eric,
Pay close attention to the socket. Make sure the bulb is actually contacting where it is supposted to. Sometimes the socket gets worn (or has been damaged) to the point where the bayonet pins on the bulb do not align the bulb correctly. You will get a short or open circuit if this happens.

Also, take the bulb out and check the output at the pins with a mulitmeter. Check for brake and taillight power. If it's all there, then suspect the insertion of the bulb.

This very problem happened on another car of mine. The PO had forced the bulb into the socket, and deformed the bayonets.

ebrownson · 11-24-2001, 10:17 AM

Doug:

OK, I get 11.93 volts on the parking light copper prong when the lights are on and 0.00 volts when the lights are off. I also get 11.93 volts on the brake light copper prong when the brakes are applied and .23 volts when they are not pressed. Don't know why it doesn't go to zero. Another problem I have is one of the metals tabs that holds the ceramic plate into the socket broke off when I was trying to remove the ceramic plate so it won't stay in place now. If the ceramic plate shifts slightly it shorts out and blows a fuse. It lights up the 21w brake light and blows the 5a fuse. I may have to epoxy the plate in place.

Can I get a new ceramic plate at any local auto parts store or are the ones on 911's specific to Porsche? Thanks for the advise, I think you got me looking in the right place now.

Eric
83SC

Doug Zielke · 11-24-2001, 12:39 PM

I think the little disc (ceramic or phenolic) the contacts are mounted on is a pretty common part. There's a spring behind it that probably should be replaced as well. I've seen these parts at NAPA and similar stores.

ebrownson · 11-24-2001, 12:56 PM

I suppose saying it was ceramic was in error. It looks like curcuit board type material. I took it to a NAPA parts store and the guy there looked like a deer in headlights when I showed him the piece. He said they didn't carry them. I will have to look around a little and may even have to try a Porsche Dealership. It looks like a pretty common part. Anyway Doug, it looks like you were on target about the cause of my problem. I just broke it a little more when I tried fixing it! Thanks for the directions. I will try to let you know if I fix it.

Eric
83SC

Doug Zielke · 11-24-2001, 03:17 PM

Quote:

Originally posted by ebrownson
.... I just broke it a little more when I tried fixing it!....

Heh, heh, heh!
That's why I say:
"If it ain't broke...we'll help you fix it 'til it is!"

I'm surprised NAPA don't have. Some stores are better than others. Maybe Manny, Moe, and Jack or some such. What about a Bug shop?