Brake lights working TOO well....

[Coonass77]

Hi guys. Brake/running light electrical gremlin issue for y'all to ponder on a 2004 M1123...

With my light switch in STOP LIGHT position, I have no marker lights, brake lights, tail lights, turn signals or flashers.

With my light switch in SER DRIVE position, all the lights turn on - marker lights (as they should), headlights (as they should), brake lights (not tail lights), and the turn signals/flashers do not work.

So basically, in STOP LIGHT, none of the lights turn on or flash and in SER DRIVE, the brake lights stay on all the time and nothing flashes when it should.

I have a buddy with a humvee that all the lights work exactly as they should so I swapped his light switch, turn signal/flasher switch and flasher module with mine and my lights still behave the exact same way. I did not swap the brake switch, but I confirmed wires 75A/B are open when the brake is not pressed and have continuity when the brake is pressed. Him and I are both running incandescent (non-LED) lights.

My guess is that there are wires crossed somewhere in the main wiring harness and my next step is to start verifying that the wiring numbers going into each connector are the same wire numbers coming out of each connector. But I thought I'd ask this group if anyone has ever had a similar issue or had suggestions of where to start looking.

I've had this issue since I picked up the truck from GP a few months ago, so I don't know the last time the lights were working properly.

Thanks for any help/suggestions!

 

[Barrman]

I think you are on the correct path. Someone plugged the rear light buckets in wrong and they probably just need to be corrected is my thought.

The flasher box is very delicate and doesn’t like stray electrons so do not use your blinkers to check for current at the light buckets.

 

[Action]

Sounds like the rear park lights burned out and someone just swapped that wire with the brake light wire just to have working lights.

 

[Coonass77]

Thanks for the replies. Unfortunately, no dice. I verified all the light bucket wire numbers (front and rear) are plugged into the correct corresponding wire numbers on the vehicle harness. I also unplugged the hood harness from the main harness to rule out the issue being in that connection, but the rear lights still behaved the same - no turn/flash and brake lights lit constantly in the SER DRIVE position with no lights on at all in the STOP LIGHT position. The signal bulb in the turn signal switch also never lights up.

I'm running out of ideas. Will gladly buy someone a beer or coffee if they can point me in the right direction!

 

[Action]

light bulbs mixed up behind lenses? if the higher watt bulb is lit with park, you may not notice a dim flashing bulb ??
3-lever light switch or push button?

 

[Milcommoguy]

Do the front left / right lamps work ? as in flash /turn ? Have you taken a peek into the lamp buckets/housing? and what did you see? Sounds like you have an understanding of lighting... just need to drill down a little more. Pull the prints from the TM's to refresh the brain cells.

There are grounds on the buckets? Do you have the plastic housings style (the two bolts that hold them) and the STRAP needs to be there for the ground or you will have a ground looping issues. The not flashing / blinking is strange too. This is a doesie ?

Need some more clues, CAMO

 

[Russ Knight]

Squirrels.