WyattsRide

Here's my symptoms:

While driving on these smooth PA roads when I hit a bump, the Stop Lamp (SL) warning and the Central Warning (CW) light comes on. When I hit the brake they both go out. While driving let's say on the Turn Pike the brake isn't used that often. (There are many bumps!) When I clear the CW light the SL warning will stay on.

The second part of this, is that this only seems to happen or it seems to happen more often when the car is warm. Not engine warmed up but the whole car itself. When I first take it out the SL warning light doesn't "bump" on. I can drive 30 or more miles and it won't happen. But later in the day if the car sits out in the warm (It's been pretty sunny, warm and humid here in PA lately) it will happen and continue to happen more often as I go. Almost at every bump.

I've checked for loose bulbs or wrong bulbs and no problems there. I also did a search here but couldn't find any threads with these problems. Has anyone run into this or have any advice on what to check?

Ducman82

some times when i accel hard, i get the same thing. clean your ground post in the trunk, take the bulbs out and make sure they are all the same brand. also clean the contact points on the bulbs and the sockets. that should help greatly.

WallyP

I think that the problem is on the other end...

Sounds more like the light monitoring box is losing contact with the 15 bus (ignition power). The stop lights can't be checked unless they are connected, and they are only connected when the brake pedal is down and the lights are on. The monitoring system sets a warning when ignition bus power is applied, and holds it until it sees functioning brake lights.

WyattsRide

I'll try this. I don't think the bulbs are all the same brand. I didn't clean the contact points when I pulled the bulbs. They don't have any corrosion but still my need some cleaning.

Wally, could you expand more on what I need to check for on this?

Mrmerlin

match the bulbs,
and clean the contact points first,
also clean the side marker bulbs in the rear,
and clean the ground point behind the right quarter panel liner,
the ground point is a 10.mm bolt
add some dielectric grease to the bulbs as well this should prevent corrosion to the bulb contacts

rexpontius

I have similar issues with the stop-light warning, especially when turning power-hungy accessories such as rear-defrost or interior blower fan are turned.

Especially when idling (and lower alternator output), the stop light will occasionally come on.

Where exactly can I find the ground in the right quarter panel liner? Is it inside the trunk, or outside in the wheel well?

Second questions, where is the stop-light control box located?

cheers

Landseer

Stop light control unit is actually called the bulb control unit. It operates on the stop lights and the tail/marker lights. Its mission is to report a missing running light on the back of the car. (Has nothing to do with turn signals, backup lights or license plate lights, btw). Its not just a monitoring device. The main signal for the stop and tail/marker lights actually route through the box. 84/5/6 use the same box. It can be backward fitted into the earlier cars.

Its hidden. Passenger side package tray. Front right corner and right edge, above the brains, but attached to the tray itself. Just behind the carriage bolt that mounts the tray to the bracket on the right side of the car.

The ground point is in an inconvenient place behind the back area of the interior quarter panel, passenger side.
Hard to access without breaking the panel.

Landseer

Plug for bulb control unit shown from below. 84 car.
Unit is above the plug.
Orientation: Brains to left of picture (euro). Carpet shown is on the right side wall of the car. Front right edge of package tray is the vinyl in the foreground. Bracket is missing the carriage bolt.


Next 2 pictures are of ground point. Helps to know where it is.
Best practice is to remove the quarter panel in my opinion.
Requires a bunch of interior disassembly.
Note evidence of butchering on the tail harness.
Somebody had skinned the wires and direct-wired the lights from the battery.
My BCU was fried to a crisp. Not sure if it was cause or effect.
It is possible to completely bypass the BCU.
Very sensitive. Replace bulbs in pairs on both sides of car.
You may have a situation where you can't stop the warning.
Might be corrosion moving up inside the wires. Might be a partially failed BCU.
Kind of a pain in the butt, no matter how you cut it.

My red car just failed inspection here in VA because the tail light warning light wouldn't extinguish. Lights work, but inspection guy was being a butt head.

WyattsRide

I should have followed up on this and let everyone know my results. Sorry.

I did exactly as Mrmerlin suggested. I replaced all bulbs, cleaned all contacts and added dielectric grease to all lights around the car. I found that the rear side marker on the driver's side had a different light (smaller wattage I think) than the passenger side and had some corrosion. Upon this cleaning and replacement, I haven't had the Stop Lamp Warning problem again.

I used this chart for my 85

1985 PORSCHE 928

High & low beam headlamp
H6024
H6024ST Silverstar High Performance Lighting: the whitest and brightest Halogen
H6024XV XtraVision Halogen Upgrade: 3x brighter; 2x the life
H6024CB Cool Blue Halogen Upgrade: White Hot; Super Cool; 100% Street Legal

Parking light
5008

Front turn signal
7506
7506LL Long Life Upgrade: Up to twice the life of the standard lamp

Rear turn signal
7506
7506LL Long Life Upgrade: Up to twice the life of the standard lamp

Tail light
5008

Stop light
7506
7506LL Long Life Upgrade: Up to twice the life of the standard lamp

High mount stop light
7506
7506LL Long Life Upgrade: Up to twice the life of the standard lamp

License plate
6418

Back up light
7506
7506LL Long Life Upgrade: Up to twice the life of the standard lamp

Front sidemarker
5008

Rear sidemarker
5008

Dome light
6411

Instrument-general
2721

risaac928

Thanks guys this is good information...I think this weekend I am going to follow your steps and do some housekeeping...

PorKen

(More bulb info, 78-86)

WyattsRide

The only thing I didn't do was clean the ground in the rear quarter panel. I just couldn't make myself bend that panel cover enough to get to it. I wish there was a better way to get to it, other than completely removing the panel as shown in Chris' pictures.

Landseer

Whether you remove it or bend it back and work your hand in there like Stan suggests, its an important thing to do.

My panel is out due to water leak on this car. Picture is to show you exactly what you are after, especially if you go in Stan's way.

rexpontius

Was really happy to find this thread, my stop lamp light kept returning intermittently.

Replaced all of the bulbs today (all bulbs in tail lights L+R) and 3rd brake light on windown.
Cleaned all the ground points, and the problem is gone!

Another great (and relatively cheap) fix!
cheers