No brake Lights - where to start

[TroyHog]

First of all I would like to thank everyone here who offers great advice. You guys have helped me out numerous times and it is greatly appreciated. As I have said before I am just an old farmer who uses my M923A1 around the ranch but I do keep it tagged because I have to get it out on the highway to access another farm we have. Don't get me wrong - sometimes I drive it just to drive it! ha. In Missouri I have to have this truck inspected every other year to keep tags current and last night after welding some corner posts up I noticed that I didn't have any brake lights but did have both turn signals. Usually (in the farmer world) if you have turn signals you have break lights so I figured I would ask where to start trouble shooting. On the light switch there was a stop/break position that yielded no lights at all, and I wasn't sure about that either. I had the switch on service lights.

Thanks

 

[mdemars03]

If your other lights work I would check the brake light switch. It is a pressure operated diaphragm type switch that actuates when you press the brake pedal. I believe it is on the driver's side frame rail kind of near the fuel tank. It is a small round part that is plumbed into an air line and has 2 wires coming out of it. Get a meter and have someone press the brake pedal while you watch for a change in voltage. If no voltage change most likely a bad switch. Also they can be removed and cleaned if you have dirty contacts inside. If you do try to open it up and clean it just be careful not to damage the diaphragm inside or else you will definitly need a new switch even if that isn't the problem.

 

[mdemars03]

The switch should look like this...

 

[TroyHog]

Is this the brake light switch?

Guys - still trying to figure out why my brake lights will not work after I hooked up a trailer. Could be coincidence I guess. I can not find anything likely candidates except for this one. It is on the left frame rail about half way back. Can you guys confirm/deny this for me? Thanks.

 

[Swamp Donkey]

Yes, that is the brake light switch. To test, unplug both wires and connect them with a jumper, then turn the 3 lever switch on the dash to the Stop Light position. If you have brake lights with the wires jumped, then your switch is bad.

 

[simp5782]

Guys - still trying to figure out why my brake lights will not work after I hooked up a trailer. Could be coincidence I guess. I can not find anything likely candidates except for this one. It is on the left frame rail about half way back. Can you guys confirm/deny this for me? Thanks.View attachment 654210

You may have a short on the trailer and it popped one of the breakers up on the firewall

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[TroyHog]

Brake Light Switch

Can you guys tell me where I can get a brake light switch? Thanks!!

 

[simp5782]

Can you guys tell me where I can get a brake light switch? Thanks!!

You can try a surplus supplier. If its on a 939 truck you can use Napa BE13250 and crimp on eyelits in place of the military connectors.

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[porkysplace]

Can you guys tell me where I can get a brake light switch? Thanks!!

Most any of the vendors that advertise on this site ,e-pay , napa.
Google the part number from the parts TM and it should give you several options.
Not knowing which model 5 ton that's close as I can get .

Googling " brake light switch for M??? " should get you some results (fill in your M series number in place of the question marks)

 

[TroyHog]

Thanks Guys!!