My 1995 TA started having an issue last year. The rear marker lights stay on when the weather is warm after I turn the car off. Pressing the brake petal brightens them up more - so its not the brake switch. This of course drains the battery. Removing the brake/marker fuse stops it. And later, when reinserted later after the car cools down, the problem goes away,. I've replaced the flasher solenoid.

I've looked at the wiring diagrams and not sure what to do next. There must be a short somewhere - just not sure where to start. Digging under the dash has got to be one of the worst things to do on this car.

Suggestions ?

 

Leeman,

Have not seen that problem, but almost all mystery light problems are caused by corrosion at or in the external light fixtures, not by the wiring under the dash. Not a surprise, in a twenty year old car.

Since you have the wiring diagram, look for a wire having power normally, with the car OFF. Check all around that wire at the fixture. Rust and corrosion there or in the bulb sockets may be the problem.

The auto parts stores will have a small "wire toothbrush" that is good for removing rust from fixtures. A rust dissolver solvent can help, but wash the fixture with water after that.

 

I'll take a look at the rear lights, but I doubt there is any hot lead that runs there and also pulling the hazard/brake fuse stops it.

 

I passed over this one at first because I didn't understand it. GM calls the clearance lights on the sides of the fenders "marker lights". But I think you are asking about the rear lights that GM calls "taillights"?

If you are in fact talking about the taillights, which bulbs stay on? There are three bulbs on each side. one bulb is a single filament, and only lights with the taillight. The other two bulbs are two filament, with the taillight on one filament and the brake lights on the other. If the taillight filaments are staying on, they get power through the headlight switch. If there was a faulty contact in there, the front parking lights, rear side marker light, and license light would also stay on. Do they? If so, check pin "C" on the headlight switch for voltage when the switch is in the "OFF" position.

 

Thanks Fred ! I'll try to recreate it (it doesn't always happen) and take a closer look. I do know that pressing the brake pedal makes them all light up brighter as well as light up the top brake light.

 

Sure, that’s normal when the brake pedal is pressed. But I don’t think that is related to your problem. The single taillight filament is on producing one level of light. When the brake pedal is pressed, the second filament in the 2-filament bulbs light up, increasing the brightness of the light. Focus on why 12 volt power is reaching the taillight single filaments, when the parking lights or headlights are not switched on.

 

So, finally got around to debugging this issue. The problem ended up being the brake switch (attached to the brake pedal). The switch has 2 trigger points - the first basically lights up the rear "parking" lights. The second level when you press harder lights them up brighter and also includes the 3rd light.

Biggest problem I ran into is there are several different parts available for 4th gen f-bodies for the switch. My 1995 apparently uses the 93/94 switch. They don't make them anymore (surprise), but I found someone on ebay who has a box of them in Houston.

 

How did you figure this out. Never noticed this on my 94.

I looked in the 95 factory service manual and couldn't find any indication of a 2-stage brake switch. There are two internal switch contacts shown, but they are shown linked together and appear to operate in parallel. One wire feeds the turn/hazard switch assembly, the other wire feeds the center high mounted stop light and the EBCM control circuit. The 94 factory service manual has the same diagrams as 1995 (we know there was at least one case - coolant fan controls - where the 94 diagrams showing "early" and "late" schemes were carried over to the 95 manual).

 

I narrowed it down to the switch when I came home one day and noticed the rear lights on after I closed the garage door. Feeling under the dash, the switch was hot, and the rear lights would go off when it
was played with. I also noticed that when you depress the brake pedal (or switch), the rear lights had two settings. The second being brighter and including the 3rd brake light. Also, the switch itself has 3 terminals which should enable this.

 

The third terminal connects to the auto trans, not to any lights. It unlocks the torque converter when the brake pedal is pushed. If the vehicle has a manual trans, the third terminal is not utilized. That circuit is normally closed, and the circuit opens when the switch I depressed.

1995 4th Gen F-Body Exterior Lights

 

Go look at your diagram again. The third terminal goes to the 3rd brake light to the right. The auto switch is a different connector that is not used or connected on a manual tranny car.

 

It isn’t my diagram, it's from the factory service manual, and reproduced on Shoebox's site.

All 3 switches in the “Brake Switch Assembly” are linked together (dotted line) and move in parallel. There are only two “dots” for each switch, representing the internal contacts. Switch to the right dot = open circuit on both. Switch to the left dot = closed circuit on both, simultaneously lighting the left and right brake lights (via the turn/hazard switch assembly), and the high center mounted stoplight. There would be additional “dots” on the switch schematic if there was an intermediate circuit activation.

Additional wiring for brake lights…. The “A” in the triangle connects to the stop lamp filament in the driver side, the “B” in the triangle connects to the stop lamp filament in the passenger side. Additional detail is shown on factory service manual page 8 A-110-5.

1995 4th Gen F-Body Exterior Lights