smokindog

Fellas,

My brother has a '90 Chevy 1/2 ton without brake lights or hazard lights at the moment. He's only 20 so, of course, it all of a sudden just "happened"!

It has the standard 3057 dual filament bulbs. The top bulb appears to be the one that will light the second filament when the brake pedal is depressed, but when I hook up the multimeter to it I get 10.86v from just the taillights, but no increase in voltage when he depresses the pedal. Does this point to the switch on the pedal itself? It's only a $15 part, but I don't want to throw a part at it and not fix it for him.

Thanks in advance for any help you can lend!

DMH

I apologize for not being an "electrical Guru" and for thinking "out loud" here.

My son once had a car that did not have brake lights and he was in a turmoil, thinking he was going to have to rewire his car. I went out with a multi-tester, pulled a bulb and checked the continuity on both nubs. Good on one, nothing on the other. Bad bulb. Checked the other one, same thing. Both bulbs had one bad filament, thereby, no brake lights.

If you were reading 10.86 volts on the taillight side of the socket, you will not see an increase on that side when the brake pedal is pushed in. You should see some voltage on the other nub in the socket when the pedal is pushed.

How about the fuse, did you check to see if there were any fuses labeled for brake lights? There might be something else "attached" to that fuse that will not be working as well.

Just a couple of thought here. Good luck.

DMH

smokindog

Yeah, I checked the fuse and also popped 2 new bulbs in there. My genius brother did have one of his moron "friends" fiddling with his stereo and now it is on a constant hot wire so it could be the same wire as the brake switch.

So what you are saying is that I should check the voltage with one bulb in and the other out? I have not checked continuity yet, suppose that would be a good idea!

Mopardan

I had problems several yrs ago with the brake lights on a car. Found the ground wires had worked loose. Don't know if that applies to the newer vehicles tho.

smokindog

Yeah, I checked the darned ground wires too! I am stumped!!!

DMH

If you look at the base of those taillight/brakelight bulbs, you will see two nubs on the bottom. One of them is for the taillights and the other one is for the brakelight. They are two seperate curcuits in one bulb. In the socket, you will see the matching nubs for the ones on the bulbs. It is grounded through the base of the bulb to the socket itself.

You can check the bulbs by using a continuity checker, using one probe on the base of the bulb and the other probe on each of the nubs on the bottom, one at a time.

You can check the nubs at the base of the socket using a regular 12v curcuit tester. Clamp the ground to a good ground on the vehicle, turn on your parking lights and touch each of the nubs in the base of the socket. One of them should light up your tester. Turn off the parking lights, have some push in the brake pedal and touch the other nub. It should also light up your tester. If not, then you have a problem somewhere further up the system. You will have to trace the wiring all the way back to the fuse to find it. I know, time consuming, that is the way I do it.

DMH

fschiola

If no luck with the advice from the previous posters, undo the rocket scientists wiring from the stereo and see if that helps. He may have caused the stoplight switch to be always closed.

smokindog

That's where is was going next. I'm waiting for my brother to join the land of the living now. Some days he doesn't get up until 1600 or 1700 Then other days, like yesterday, he is actually early to the office and alert all day long at work

Partsman

You say
"no hazards" front or back? Do you have turn signals?

darkvader

jumper the brake light switch, if that does not work check the flasher(put in a known good one)
Clark

torquefan

If the hazard lights don't work either, the problem could be the signal light switch. Brake light power goes from the brake light switch through the signal light switch to the rear lamps. The first place I'd look however, is under the rear bumper where somebody has spliced in trailer wiring. That's where 80% of the problems are.

Also, on that vehicle, the center bulb is the brake (and tail) light. The lower is reverse, and the upper is tail only.

smokindog

That's right, no hazards at all, but the turn signals work just fine.

smokindog

That was what I really wanted to know! How the hazards and brake lights were linked. There is no trailer wiring, no hitch either. Everything underneath and in the lamp assemblies themselves is still factory. Even the old dried up dielectric grease after 16 years!

Are you sure the upper is not a brake/tail light? Both the middle and top lights come on when the tail lights are on. Then the second filament in the middle bulb activates when the turn signal is activated. I was assuming that the top light would have its second filament light when the brake pedal was depressed. Reasoning that top bulb functions were brake/tail, middle were signal/tail, and bottom is back up lamps. I believe his manual is a Hayes or Chilton (given to him when he bought the truck) and so far none of the wires have even been the color that the book states they are supposed to be!

Partsman

I would check where the guy got the radio power from, if he used a scotchlock he could have cut the factory wire and still have power to the radio. Its also posible he screwed up the adjustment on the BOO switch. Hopefully he didn't short out the multi-function switch.

torquefan

The top bulb is tail only, the center bulb is tail/brake/turn signal. Back then they didn't have separate brake lights- that's why the power goes through the signal light switch from the brake light switch.
Hope this helps.