M35A2 brake light issues

[Vintagefarmer]

Picked up a 69 m35 this last week non running. Got it fired up, bled the brakes, all the fluids have been changed and now im onto lights. So far the issue I'm have is no service brake lights. I've got service running likes, blinkers (they stay on solid cause the flasher is shot but they do come on) I've got all blackout lights including a blackout brake light and blackout running lights. I've swapped out the main light switch as mine was a bit under the weather and procured a new turnsignal stalk. I've got power from the brake light switch to the turnsignal and I know the wiring isn't grounded out because the turn signals work... I'm positively baffled at this point and not much is making sense. The only thing I can think of it maybe a bad ground at the light but then why would the rest of the lights work fine? Is there a circuit breaker I'm missing?

I also jumped the pins at the plug for the turn signal and didn't get any activity when I hit the brakes.

Any thoughs?

 

[Mullaney]

Picked up a 69 m35 this last week non running. Got it fired up, bled the brakes, all the fluids have been changed and now im onto lights. So far the issue I'm have is no service brake lights. I've got service running likes, blinkers (they stay on solid cause the flasher is shot but they do come on) I've got all blackout lights including a blackout brake light and blackout running lights. I've swapped out the main light switch as mine was a bit under the weather and procured a new turnsignal stalk. I've got power from the brake light switch to the turnsignal and I know the wiring isn't grounded out because the turn signals work... I'm positively baffled at this point and not much is making sense. The only thing I can think of it maybe a bad ground at the light but then why would the rest of the lights work fine? Is there a circuit breaker I'm missing?

I also jumped the pins at the plug for the turn signal and didn't get any activity when I hit the brakes.

Any thoughs?

.
Silly question - but lights need to be on for the brake lights to work.
Have you done that?

The circuit does go through the turn signal (SignalStat) so that is another possibility

 

[Vintagefarmer]

.
Silly question - but lights need to be on for the brake lights to work.
Have you done that?

The circuit does go through the turn signal (SignalStat) so that is another possibility
[/thoughts?

Yup, all the lights were on, service lights on with panel on full blast.

 

[Elijah95]

Strange thing, when my flasher module failed on my m35, my brake lights failed with it. As soon as I installed a new one, it went back to working


Sent from my iPhone using Tapatalk

 

[G744]

They need air to operate, too.

DG

 

[Vintagefarmer]

They need air to operate, too.

DG

This has a fluid switch on it which I've confirmed works.

 

[M35A2-AZ]

Did you short the two wires at the brake switch on the air pack? Did they come on?

 

[jeffhuey1n]

Have you checked the function of the brake light switch on the air pack/master cylinder?

 

[Vintagefarmer]

Follow up:

I crawled under the truck and jumped the brake light switch (I know it works as I've already verified that) so I would need 2 people. I then unplugged the turn signal switch and checked for 24 volts at pin D which is the signal from the switch and had a good reading. I then jumped from pin D to both C and E but got nothing. I did replace the turn signal flasher unit and I've got full working turn signals now... I'm stumped

 

[G744]

The L&R brake lights are independent, and are routed thru the turn switch.

This allows one lamp to do two jobs: Stop and/or turn.

Many times I've come across those switches with one or more functions burned open from shorts to ground downstream.

"Things worked fine until I plugged in my trailer pigtail". Heard that more than once...

Once you get it sorted,I highly recommend installing a 10-amp fuse in the feed to the turn switch. A lot cheaper than a new switch. The full load of all those lamps is still low in current demand, but a dead short will let many Amps flow and fizzit, your switch is junk.

DDG

 

[G744]

A note: The stop light circuit also routes thru the headlight switch, which steers the power to the turn switch, or the blackout stoplight(s).

DG

 

[Al Capone]

I had one brake light not working on mine . Changed out the blinker switch and fixed it