Why did my brake lights quit working?

[jeeper]

But the turn signals work fine.

I have power at my brake light switch. When I activate the brake pedal I have voltage on both sides. My brake light switch is still good. I tried replacing the 3 lever switch with a new one that came with my truck.

When I put the 3 lever switch into blackout drive my blackout brake lights work fine.

What am I missing?

[Barrman]

Wire 75 takes power from the 3 lever to the brake switch and wire 75 brings the "brake lights on" signal back to the 3 lever. If your brake light works in black out mode and not in service mode. Along with your service blinkers ok with the same wires as the brake lights. I would suspect your replacement 3 lever is bad.

I went through 4 or 5 used 3 lever switches when I wired my M715 up 7 years ago. There was always 1 thing that didn't work. B/O spot light, B/O brakes, service brakes, dash lights on low, dash lights on high, etc. Everything else would be fine.

There is a way to take the switch apart and get it back together again. I have only tried once and couldn't get it back inside the case.

[Barrman]

Forgot to add this. Pull up the "lighting wiring diagram" from the online manual link. It shows which pin does what. Use a DVOM with a beeper if you can. Run though all the functions and make sure current flows everywhere it is supposed to. If that is good, put power down the wires to the brake lights and see if the light up. You could also have a bad blinker arm switch. Even though that is pretty rare compared to the 3 lever going.

[jeeper]

I traced it back to the turn signal switch. Now I'm asking myself why the wire melted in two.



I soldered a new wire in it's place. It's a little heavier gauge wire 'cause it's what I had on hand. I now have brake lights again but am wondering for how long?

[randyscycle]

Have you been inside the light housings on the rear?

I ask, because so many of them have been or still are full of water and the corrosion left behind or in progress can cause a number of issues.

[jeeper]

Have you been inside the light housings on the rear?

I opened them when I converted the truck to 12 volts last spring. They were clean as a whistle then. I will check them now though.