No brake lights

[Manstein]

Well boys, I had brake lights then, after picking up a M105 and checking its lights I noticed I don't have brake lights or rear turnsignals on the deuce.!? The front lights work with signals, the green light on the signal switch flashes but I got nothing on the rear. I checked the bulbs and took the light housing off the left side and sanded the surface on the back or the lamp housing and the mounting bracket and reinstalled, still nothing. I also tightened the two bolts that hold the mount arm to the truck frame. I've checked the harness for cuts or damage and can't find anything. If it's a ground why would it still have tail lights? The flasher is new... Any thoughts? I don't know that the trailer caused it, it could have been out prior and I just didn't notice.

 

[Recovry4x4]

The tail lights are grounded through both mounting bolts. One bolt grounds some bulbs and the other grounds the rest of the bulbs (can't rmember which). Using a test light check for power at the brake light sockets. If not power then check the circuits upstream until you find power. Using the schematic in the back of the -20 you can determine the circuits. I'm not sure if the turn signal switch can cause this but I suspect it could.

 

[ironhorsethegeneral]

I suspect it is the turn signal unit. It can cause a variety of problems.

 

[acetomatoco]

Yup, and it is usually a ground problem there too...

 

[L7]

because the front blinkers and parking lights are working it is more than likely your brake light switch is bad, or unplugged.

it is located on the front or side of your airpac based on your vehicle model year or latest MWO.

in any event Recovry4x4's suggestion should isolate the problem if it is some other electrical fault.

 

[Manstein]

The brake light switch was replaced a few months ago (just for general purposes) and is plugged in. That doesn't gaurantee that its working right, but its a new one.

 

[Manstein]

I hate reading posts that aren't complete. I fixed the brake light. The bulk connector under the cab had a loose pin.

 

[m-35tom]

brake light switch is only for brake lights and can never have anything to do with turn lights not working

 

[bulldog_mack13]

I tried reading this , your turn signal arm/ thing you use to make your left and right work if thats bad or not on right then your brake likes dont work? My 5 tons dont and I changes the brake light switch under the truck etc, Jay

 

[IMA944T]

I have a simliar problem. Noticed that turn signal switch was not flashing. Then checked frt. and rear turn signals and brake lights and have none. Have tail lights and headlights.

 

[shepsjeep]

One of our club members had a problems similiar to this, check the canon plug that connects to the signal unit on the column. Corrosion lurks anywhere there is a connection on these trucks, resulting in broken wires and shorts causing all sorts of strange lighting effects.

 

[dabtl]

One really good solution to grounding problems is to contact Grainger and buy a variety of the interior/exterior star washers. New star washers can cover a lot of problems quickly.

 

[cranetruck]

FWIW, you need air pressure for brake lights to work if the new (air operated) stop light switch is installed. The hydraulic switch works without air pressure...

 

[Ferroequinologist]

If your turn signals and brake lights are not working on the rear, it is either corrosion, ( in the plug on the turn signal switch or the connection between the rear harness and the front. Plug is under cab on driver side inner frame rail.) or it is your signal switch. Highly doubtful that both tail lamp grounds would go bad at the same time, and if the indicator light on the switch is working, then the ground is good there as well.

I had this exact same problem on my first truck, the rear lights just quit working (except marker) on the way to Aberdeen. Bought a used signal switch from Gimpy, and swapped them. Everything worked again.

 

[IMA944T]

My rear turn and stops quit and my frt. turn quit also. Does the turn switch have anything to do with the stop light circuit? This would seem werid but something the military might do. For all to quit at once is strange. Does the master switch for routing everything ever cause problems? New to these as I am I wonder does the master switch have a position for running head and tail lights only without trun and stop lights?

 

[cranetruck]

Perhaps the best wiring diagram for the turn signals that I have found is from the M809 series -20....

 

[dabtl]

The stop and turn signals are separate circuits. For the turn signals, the first thing to do is see if the light on the turn signal controller is lit. If it is, you have a ground there. Then check and clean the grounds on the turn signals and flasher. If you have grounds working on all the signal lights, a good flasher and the turn signal controller lights, you should have signals, assuming you have power to the circuit.

If all the grounds are good to go and no blink, a bad flasher is the problem.

 

[Ferroequinologist]

The brake lights go through the turn signal switch, as the bulbs are shared for turn signal and brake. You can see that in the wiring diagram Bjorn posted. That's why if your making a turn you can step on the brakes and the one will still flash while the other is steady.

If they were seperate you wouldn't have that, they would both burn steady when you put on the brakes, even if you had the flasher on. Yes, the front ones are controled through the turn signal switch as well. The front and rear curcuits are seperate in the switch.

IMA944T the main headlight switch does not have a position for running headlights and marker lamps only. There is one for all the markers, but the brake and turn lights will still work. They didn't want you driving the truck without the brake lights, so any position other than blackout (and even in black out ther is a 'brake' light) and off you have brake and turn signals.

 

[tjcouch]

Anyone know where the air pressure operated brake light switch is usually located?

 

[Ferroequinologist]

Near the air pack, on the J line if you have the new style, or on the hydraulic line off the MC if you have the old style.