brake lights

[lindbergh]

Need some help. While working on my brake light boards today, I shorted out one the boards and the brake lights went out as the fuse did it's job and blew. What I don't understand is why when I replaced the fuse the brake lights still don't work. The board I was working on is totally disconnected and I would expect the brake light I didn't touch to illuminated once again. I apparently don't have power as there is no power at the brake light switch. Any suggestions, I'm stumped. Thanks.

[Rich]

First, be sure that you really have "no power at the brake light switch". A 12V test lamp probe connected to a known-good ground point will verify it.

From there you'll have to work upstream until you get 12V+. The next point upstream from the switch is the output side of the brake light fuse at the fuse box.

Check:

• The replacement fuse is good (continuity-check it).
• There's 12V+ on the feed side to that fuse (again, use a test lamp).
• You are dealing with the correct fuse position/receptacle in the fuse array.

[David T]

First, be sure that you really have "no power at the brake light switch". A 12V test lamp probe connected to a known-good ground point will verify it.

From there you'll have to work upstream until you get 12V+. The next point upstream from the switch is the output side of the brake light fuse at the fuse box.

Check:

• The replacement fuse is good (continuity-check it).
• There's 12V+ on the feed side to that fuse (again, use a test lamp).
• You are dealing with the correct fuse position/receptacle in the fuse array.

It is a very simple circuit. Did you replace fuse #18? That is ONLY for the brake lights. From there the power goes to the brake switch and then on to the lights. If you do not have a good ground you may think you have no power when, in fact, you do have power but no way for it to get to ground. Time to get a meter or a test light and see what you really have. Maybe the bulb in the other board is NG?

[lindbergh]

First, be sure that you really have "no power at the brake light switch". A 12V test lamp probe connected to a known-good ground point will verify it.

From there you'll have to work upstream until you get 12V+. The next point upstream from the switch is the output side of the brake light fuse at the fuse box.

Check:

• The replacement fuse is good (continuity-check it).
• There's 12V+ on the feed side to that fuse (again, use a test lamp).
• You are dealing with the correct fuse position/receptacle in the fuse array.

Ok, I have no power at the brake light switch and no power at the fuse box for brake lamps only, all other fuses have power. What is upstream of the fuse box?

[rdarlington]

Ok, I have no power at the brake light switch and no power at the fuse box for brake lamps only, all other fuses have power. What is upstream of the fuse box?

Can you test the brake switch itself?

[Jonathan]

Ok, I have no power at the brake light switch and no power at the fuse box for brake lamps only, all other fuses have power. What is upstream of the fuse box?

1) you might have possibly used a bad fuse as your replacement.

2) you might have coincidentally pushed out the connector on the underside of the fuse box when you did your fuse replacement. Or something else got bumped or loosened while in there.

Is everything in your fuse and relay area a stock set-up, or do you have some retro 80s creativity in there?

[lindbergh]

The fuse is good. The wiring is original OEM. The only wiring I added was for the cruise control. The connectors are visible in the fuse box so I am guessing that means they didn't push out. I tested the voltage with the two leads on the brake switch disconnected to eliminate the switch from the mix. I started to lean toward that when the 10 amp fuse blew it took the fuse assembly with it. All the lights on the other tail assembly work except the brake lights. I guess the next step is to jumper 12 volts to the #18 fuse and see if they work.

[Bitsyncmaster]

Your fuse may be up in the harness by the brake pedal. Mine is up there but your vin is a little later than mine. Did your brake lights work without the key on?

[Jonathan]

Your fuse may be up in the harness by the brake pedal.

I don't know much about aftermarket cruise controls, but would the brake lights power wire been routed to some other spot or control box prior to the fuse relay area? Cruise controls need to know when you hit the brakes, so maybe there are extra fuses? Is this what you meant, Dave, by the harness by the brake pedal, or are you mentioning something factory that isn't to do with the cruise control? There seem to be random inline glass fuses in our cars here and there discovered when doing troubleshooting work...

[Rich]

Ok, I have no power at the brake light switch and no power at the fuse box for brake lamps only, all other fuses have power. What is upstream of the fuse box?

In case you still need this answer go to this link and scroll down to Tail Light Circuit, where the brake light wiring/colors/fuse are all shown:

http://dmctalk.org/showthread.php?40...ing-Schematics

Upstream of the hot side of Fuse 18 is main power feed. For lots of things besides brake lights, things that apparently are all OK in your car.