Electrical No brake lights

[keel]

I have no brake lights in my 1993 hatch. I did a bunch of testing, and I have power to the brake light switch and to the fuse, my fuse is good, and my bulbs are good. I thought that I might have a faulty brake light switch so I jumped the connection on the connector but still no lights. I also tested for ground and the ground connection is good as well. All of my other lights work flawlessly. I am now at a loss as to what could be causing the issue.

The car was formerly a 2.3L that has since been converted to a 5.0L but as far as I know that doesn't have any effect on the brake light circuit.

 

[AeroCoupe]

So was it during the conversion that they stopped working or some other work was done to the car or was it just an all of a sudden thing?

 

[rednotch]

If you have power to the fuse and after the switch. Stat checking the connections in the wiring to see where you not getting power... Bulbs are easy to test with a power tool battery if you don't have a power probe... so if the switch is good and the bulbs are too its in the wiring..

I had one car do that with the tail lights, not the brake lights though... Morons who installed the alarm to tap into the lights Used scotch locks and it eventually cut threw the wiring was fun getting pulled over for that one and told to turn my %$*( lights on when they all.ready where lol.

 

[keel]

The 2.3 to 5.0 conversion was done a couple years back, the brake lights stopped working unrelated to any work I was doing on the car. I've been doing some more research and I'm led to believe that it might be the multi-function switch but I'm not sure. Can anyone weigh in on this?
Really hoping I'm not gonna have to go through the harness looking for bad wiring.

 

[AeroCoupe]

I don’t believe the brake lights pass thru the multifunction switch. Quick test to ensure good grounding: remove one of the brake lights, take a test light and attach the alligator clip to battery hot, now use the pointed end and touch the ground lead on the brake light bulb receptacle. If it lights up you have a good ground.

 

[Pinellas50]

The brake lights absolutely go through the turn signal switch. You can back probe the wires in and out of the switch at the column connector to verify or rule out.

EDIT: The more I thought about what I wrote the less confident I am on it's accuracy. The turn signals and brake lights are seperated on these cars so there may be no need for the brake circuit to go through the turn signal switch. I haven't been able to find a wiring diagram to confirm/deny. Sorry if I have bad info.

 

[keel]

I replaced the multi-function switch and that did the trick

 

[AeroCoupe]

Pinellas50 for the win! Now I am going to have to look through the wiring diagrams for my car this evening. Never would have thought the multifunction switch would have had anything to do with the brake lights.

 

[Mustang5L5]

I don’t see where it goes through the MFS.

This is the 87-89 diagram, but it looks like they may share the same fuse (Fuse #1) but then it splits

 

[keel]

My car is a '93 model, maybe it is a little different? I believe in my car the brake light and turn signal light are the same bulb. My guess is that the multi-function switch handles situations where the turn signal is on and the brakes are applied at the same time.

 

[AeroCoupe]

I will pull the wiring diagrams for my 93 when I get home and post up the section on the rear tail lights. I want to say the outer part of the lens has a small running light and then a two filament bulb for brake and turn, and then the two upper clear lenses are the back up and hazard. The tag lights are either in the trunk lid or hatch.

 

[keel]

I'm pretty sure the running light, brake light, and turn signal are all the same bulb. There are two filaments, a dim one for the running light, and a brighter one that functions as both the turn signal and the brake light.

 

[Mustang5L5]

Here’s the 90-93 wiring diagram. Same setup really. Doesn’t go through the MFS

 

[keel]

I work at an auto parts store and I did some investigation in the catalog. It looks like there are two different types of turn signal lights that could have come on the car, and they have to be compared to the original lights to verify fitment. This leads me to believe that the cars came from the factory with two different possible tail light set ups, one where the turn signal light shares a bulb with the brake light, and one where they are two different bulbs. In either case, the running light and the brake light share the same bulb.
This would explain why in some cases the circuit for the brake light would need to go through the multi-function switch and in some cases it would not need to.