Yeah, like the time my A/C stopped working and I surmised it was probably that underspec'd relay. Carefully unsoldered the original and spliced in the heavy duty replacement. Uh, no-go. Should have checked the freon first. Doh!

 

My errant and persistent light was caused by the lamp controller. The inside was badly corroded. It was the last thing i checked/replaced after going through all the light connections, wiring and bulbs 3 times.

 

I almost did that too. The problem kept nagging at me and it took two more spelunking trips with the multimeter(trying to prove to myself that the head unit WAS the problem) before I realized that the problem was actually an open circuit in the fuse panel itself.

 

I will have to check the side markers and license plate lights? Hopefully its one of those! Luckily for my friend he is not a perfectionist like me, so he can live with an annoying warning light that would drive me crazy!

Perry
Sounds like you have a very annoying gremlin in your system somewhere. Maybe you should try pulling the pod and cleaning the connections? I heard this causes odd warning lights sometimes?

 

My light switch came in from 928 INTL about a week ago.
I've done EVERYTHING else, and am hoping this resolves this warn problem.
Will swap it out tomorrow.
Black tape is currently residing over the taillight warn and master caution.

 

Oh Yeah!
SilverSFR,
Someone should snap up that used LCU ... that's a damn good price!
I replaced mine as well ...same result...nada.

 

John -- EVERYTHING else?

 

Mine did that for the first time tonight after going through the car wash. It comes on immediately after starting the car and turning on the lights. It goes off after about a minute of driving. I'm guessing I got a wet socket.

 

There were a few mis-statements in this thread...

The "Tail Light" warning and the "Brake Light" warning are very different.

The normal action for the "Brake Light" warning is for the warning to be on after the engine is cranked until the brake pedal is pressed. If the bulbs are good, the warning then goes off. The only bulbs that affect this warning are the brake lights in the tail lamp housing and the CHMSL (Center High Mounted Stop Lamp).

The "Tail Lamp" warning can be affected by the tail lamps, side marker lamps and license plate lamps. This warning may come on at any time after the parking lamps (or head lamps) are turned on.

The Bulb Check Unit is located between the glove box and firewall on most cars. It is different from the Central Warning Computer, which is located in the dead pedal in most cars.

 

Wally, in my case, which one, the bulb check unit or the central warning computer is most likely to be my culprit.

 

Thanks for the corrections, Wally. Isn't the lamp control (bulb check) unit below and to the sidewall side of the glovebox (above the LH brain on later models)? I think it's mounted on the end of the passenger package tray in my 89. The box between the glovebox and firewall (i.e., behind the glovebox) on my car is the alarm control unit. The central warning controller is under the dead pedal, as you said. It still may be involved in false bulb warnings, as I recall.

 

I went round and round with this when I first got my car. It turns out(at least on my 78, and allegedly on all sharks) that the front parking lights in the bumper can cause a tail lamp warning. The problem went away when I replaced those two and cleaned up the sockets and connectors.

 

Hi on my '84 S2 I had a problem with a working/non-working tail lamp for a long time. I tried to clean the contacts of the bulb several times, also cleaned the 9pin-connector inside (next to rear fenders, hidden under the interior panel). I did measure a voltage on the bulb contact, but not a very stable one.
The problem was an unstable contact in the light control unit (bulb tester). The light control unit is screwed to the lower compartment on the passenger side and can be opened easily (4 little screws hold the housing together). There are no mechanical parts or relays inside, just relatively big coils and resistors.

Save the 200 $ for a new light control unit, it can be repaired by re-soldering everything on the print and also soldering the contacts to the print, which are pressed together.
Cheers Thomas

 

A similar problem in mine last week was a broken wire in the hatch. Since the tool kit pushes down on those wires, one of them had rubbed the metal clip that holds the harness and cut it in half. Something to look for if you get the "tail light" warning.

 

The bulb contoller will set off the warning light if it detects increased resistance from one side of the car in comparison to the other side. So, all the lights can work visually, but if there is corrosion on one of the sockets, or bulbs, the warning light can still light. This frustrated us, too, until we fiqured it out. Pretty much need to clean all the sockets and replace all the bulbs (clearance, taillights, and license.) Make sure the bulbs are all rated correctly. We've had cars where a different amperage bulb was installed in one socket. Of course the computer detects this as increased resistance and sets off the warning light. Again, hard to detect, since all the bulbs light.