I looked through this forum to see if anyone else had this issue, but couldn’t find any. I have an old 1994 Peterbilt 375 (tractor/trailer) converted into a dump truck. I replaced the head light socket and fixed the panel light bulb. But now my brake lights are always on. I don’t think what I did cause this problem and the brake lights in the past were never a problem. I looked under the hood and have no clue where to start looking. I am guessing that it is a problem with pressure electrical switch and I don’t know where to look to find it. Any clues?
Turn your hand brake valve off[trailer brake],if you still have one. Bob
+1 Check your spike. I've done that before.
I'm a nubie at this stuff. It looks like all the old plumbing for the trailer is still there. Where would I find the hand brake value and what is a spike?
That's Ok Ranch Hand, ya gotta learn somewhere. The hand brake valve is that lever on the right side of the sterring column, it applies the trailer brakes [by hand]. Many times when you pull a dash panel out to perform a repair, such as replace a gauge bulb, you'll hit the hand brake valve and move it slightly in the apply brake position. This turns on the brake lights.
That lever is there. Never knew what it was for. I am guessing it might be disconnected or something. When I checked the truck today I turned on the ignition and moved that lever up and down and the lights didn't come on. I can check it again to see if I can get the lights to come one, but it will be a while before I'm back at the ranch. If this is the cause then I breath a sigh of relief that I'm not looking at an expensive repair job. Thanks for all your help, this forum is great.
You have to build up air pressure to make brake valve,lites work. Bob
Yup, a spike is a term for the trailer hand valve. You will need air pressure in the system to check it. Usually on the petes, you undo the screws on the dash panels and tilt them back and rest it on the wheel to change the bulbs. This is when the handle gets pushed. If your still having issues, crack a brake like at a chamber and see if there's air in the line when the pedal is released. What can happen with any truck with a few miles on it is the piston in the treddle (foot) valve gets seized inside the valve. The brake light switchs need very little air to turn the lights on (as low as 5psi). So what can happen is you press the brakes, the piston sticks a little bit, you still have 6 psi in the brake lines. You would likely never notice the brakes dragging but the lights will stay on.
Just a quick update. Yup thoses controls are still active. Got up to the ranch and checkout that lever. Brakes lights go on when pulled down, goes off when pushed up. Thanks for all your input. Big sigh of relieve I don't have an electrical issue to repair before my state inspection. Thanks again.