M929A2 Dump Truck Brake Light Problem

[dsmith006]

Hey guys! I'm back again, y'all helped me a lot last time with a throttle cable issue and a fuel tank swapping valve.

This time I've got another problem, my brake lights won't work! When I turn the switch to lights, everything seems to work fine, except the brake lights.

I'm not sure if the two red lights in the back are supposed to blink like turn signals, but they don't...(I would think they're supposed to).

I've got a manual on the truck, but I think it might just be an owners manual, it goes into detail on lots of things, but I can't find a complete wiring diagram for it.

Do these trucks have fuses in any particular location? I've traced all sorts of wires and see a fuse randomly placed but haven't found a fuse box.

I read on another post about checking the brake light switch on the inside of the frame rail, so I disconnected that and shorted the two wires, but still no brake lights.

I'm sure you guys have got a few things I can try!

Thanks very much!
David

 

[porkysplace]

Hey guys! I'm back again, y'all helped me a lot last time with a throttle cable issue and a fuel tank swapping valve.

This time I've got another problem, my brake lights won't work! When I turn the switch to lights, everything seems to work fine, except the brake lights.

I'm not sure if the two red lights in the back are supposed to blink like turn signals, but they don't...(I would think they're supposed to).

I've got a manual on the truck, but I think it might just be an owners manual, it goes into detail on lots of things, but I can't find a complete wiring diagram for it.

Do these trucks have fuses in any particular location? I've traced all sorts of wires and see a fuse randomly placed but haven't found a fuse box.

I read on another post about checking the brake light switch on the inside of the frame rail, so I disconnected that and shorted the two wires, but still no brake lights.

I'm sure you guys have got a few things I can try!

Thanks very much!
David

You need a test light to see if you have power to the switch , eliminated the problem that far .
Wiring diagram is in here M939_P2P.zip

 

[Carlo]

Try the easy things first as in checking the bulbs.
Then go to the switch under the dash / pedal fire wall I think you call it sending unit? had a 931A1 that I had to change it out.

 

[73m819]

The turn signal/brake light are the same bulb, change each bulb in both housing (top bulb, Does the front turn signals work, if so, you are getting power to the switch,

 

[dsmith006]

Holy Crap! Thanks for that download! That's some crazy good info!!

The blinkers do work in the front, but I haven't checked the bulbs, I need to do that. I just figured the chances of both of them going at the same time were unlikely!

 

[Coffey1]

OK the brake light was not working on my M923 .
Checked stop light pressure switch it was OK.
Checked blubs they were OK
Tried checking switch by doing TM tests but could not read the letters on plug or switch dang bi-focals.
So I had my old switch that I had changed out thinking it was bad on another issue.
Put it in and all is good. All lights work including stop lights.

 

[lindsey97]

brake light pressure switch is on the inside of the frame, on the left side, just past the back of the transfer case. has two Packard connectors plugged into it.