Hey all,

Recently I realized that my brake lights are not working on my '86 trans am. However, the hazard lights as well as the blinkers work, just not the actual brake lights themselves. The only recent work I did was pulling the carpet up to install SFC's and taking the carburetor off. Has anyone had this problem? How would I start diagnosing this? Thanks.

 

You might start by checking the fuse. There's a different one for brake lights vs turn signals.

 

If you are talking about the 3rd brake light (CHMSL: center high mounted stop lamp)...

There are electrical connectors that go onto the rear-glass gas-shocks... and get knocked-off very easily.

 

failed brake light switch maybe?

 

I'll take a look!

 

I was talking about the brake lights though my third one has never worked. I'll check if that is the issue.

 

I saw that in another thread, ordered one to be transferred to our store at work (benefit of working at an auto parts store) incase that is the issue.

 

So I replaced my brake light switch, fuse, and one of the bulbs (which looked to be in decent condition) to no avail. I'm going to pull my carpet tomorrow and make sure I didn't drill through a wire or anything when installing my SFCs. Also, could lack of brake booster pressure cause this? I recently took the carb off for the first time and it worked before. Thanks.

 

Are you not checking for 12v+ and 12v- anywhere?

 

I have not checked yet. I am going to go try the fuse. How should I proceed after that? I'm pretty clueless when it come to this kind of stuff.

 

12v test light can be used at any connection/ terminal in the circuit that you come across.

Work your way across the circuit from power towards the device being powered:

Battery, Fusible Link, C100 bulk-head, Fuse Panel, Fuse, Head-Lamp Switch, Head-Lamp Connector, Etc...

 

I don't have a 12v test light though I will pick one up tomorrow. The wiring shows that the stop/ hazards go through the same fuse. So fuse, then brake light switch, then bulbs? Could it be due to me messing up a ground when I lifted the carpet up?

 

Also on a side note, previously the brake light on the dash would be on regardless of whether or not I had the emergency brake pulled or not. This seems to have fixed itself at the same time my lights themselves stopped working. Could this be related?

 

Anything is possible... I have no idea if the wiring in your car has been altered.

The brake combo-valve has a switch in it that can turn on the brake warning light...
I would take a look at it.

 

The switch on the MC if I’m not mistaken activates when there is excessive pedal travel, as probably experienced with your soft pedal. It’s to alert you to a potential leak or braking problem. I’d start there and make sure the brake system is in order. Hydraulic systems aren’t known to fix themselves

 

Ok so here is another update incase anyone can help me more. Tested the fuse for the brake lights (STOP HAZ 20A) with a continuity tester and it showed power going through it. Same with the brake light switch. It sends power exactly as intended, through the light blue line for the tail lights when the switch is released (or as if the brake pedal was being pushed in). Furthermore, the TAIL 20A fuse was showing no power at all. According to the diagram this is linked through a brown wire to all of the tail lights which is odd considering that the only lights not working are the brake lights themselves. Could there be a reason for this? I am going to test the bulb sockets themselves in a bit when it cools down a little outside.

 

Bulb socket turned out good except for one wire which I believe is linked to the TAIL fuse not the STOP/HAZARDS one, brake light switch turned out good, fuse turned out good. There is no break in power from that system and furthermore, the brake light switch itself is not the issue. I think it may have to do with the TAIL fuse, I replaced the fuse and it is drawing no power so I believe that it may be disconnected up front or something but my god do I wish I never had to look under the dash. Disconnected wires, zipties, and a connector that had a piece of metal stuck in it (to close the circuit I believe?). It would be incredibly helpful if anyone had the wiring for the 5.0 4bbl engine or can point out the ground locations under the hood. I'm super new to this stuff but it makes me want to pull my hair out lol. Could a bad ground be messing up that one fuse?

 

Here ya go , your 1986 5.0 4bbl wiring , and also your 1986 lighting circuits diagram ....