Turn Signal / Brake Light help

[3rdmdqm]

Searched threads and didn't find anything that covers this specific combination. Lots of good info in other threads however most deal with total failure. This seems to be a partial failure. Have tried every switch position and have the same issue.

> No brake lights and no rear turn signal lights.
> Front turn signals work and the rear tail lights work.
> All other lights work including the black out lights front and rear.
> Flasher on the steering column flashes when turn signals are activated.

I ordered new brake light bulbs and am waiting on arrival to try, however I suspect the bulb may not be the issue since both stopped working at same time. Suggestions?

 

[Wildchild467]

i say use a test light and probe your trailer light plug on the truck and see if any signals are getting back there. you could just put the 4-way flashers on and probe all the sockets in the plug and see if any 2 of them blink like they should with the 4-ways on. If you dont see anything, check bulbs....never over look the simple stuff. If you are in there and all bulb sockets look good, i would put some dielectric grease on all the contacts to prevent corrosion. Im all about preventative maintance. So if everything looks good up to there, i would blame your turn signal switch. I pulled mine apart and found a bad solder joint. Its pretty obvious when you tear into it. I re-flowed the solder and it works like a charm. I made a post on here somewhere that showed what the switch looked like when i took it apart.

 

[6x6guy]

It might be the light/BO controller with bad internal contacts.

 

[two.fiveM35]

I have looked and cann't find any. Do we have fuses? How are the circuit protected?

 

[Barrman]

No fuses. The 3 lever has a circuit breaker inside that will blow when it gets hot. Then, once it cools down, current is flowing again.

The current flow for the brake lights is from the 3 lever to the brake switch on the air pack back to the 3 lever and then out to the blinker arm on the steering column and then back to the rear of the truck.

I would suggest you start at the brake switch on the air pack. One of the wires will have 24V with the 3 lever on any position except off. Put it on service brakes though for this test. You can reach up over the metal shield, unplug the wires and let them hang down for easy access. If you have 24V on one of the wires, then run a jumper wire to connect it with the other wire. When jumped, you should get a spark when they touch. The brake lights should come on as well.

No power at the plug then check your levers again and if correct, replace the 3 lever or at least trace the wires all the way to the 3 lever looking for a break.

Power at the plug, but No lights and you get to go to the blinker arm plug next.

Pin D/wire 22 on the blinker arm is power in for the brake system from the 3 lever. With the brake light plug still jumped at the air pack, you should have 24V at pin D.

If you do, jump or find another source of 24V to put power to pins C(left brake/rear blinker) and E(Right brake/rear blinker). If that makes the lights work, then replace the turn signal switch.

Still nothing at the rear, then you get to follow the wires outside the firewall and under the cab. There is a connector between the front and rear harness up above the brake master. Check for power on wires 22/460 and 22/461 when you have the blinker arm plug back in and the brake light still jumped at the air pack.

If good there, then move on down to the tail lights looking for breaks. As pointed out in another post above. Turning the flashers on and going to the trailer plug is a great way to eliminate the bulbs as the problem right away.

 

[3rdmdqm]

Just pulled both brake/turn signal bulbs in the rear. Both were blown. Volt meter shows normal votage at sockets when using turn signals and brakes. Very odd that both would blow at the same time, or maybe one was always blown and I just never noticed until the other went. In any event, will be replacing both tomorrow and if they blow again I'm suspecting a short somewhere which will require more diagnostic trouble shooting. Will advise findings. Thanks for all of the info, was very informative and will aid in the troubleshooting process if the problem persists.

 

[cessnatwin]

I agree with wildchild!