reverse lights on freightliner 1991 FLD112

Discussion in 'Freightliner Forum' started by flipper66, Jun 19, 2019.

  1. flipper66

    flipper66 Bobtail Member

    Jun 19, 2019
    Got pulled over by DOT For an inspection. everything checked out except one of my tail light bulbs, and my reverse lights aren't working. the Tail light was easy, I must have backed in too deep and cracked the housing, which cut a wire on it. I replaced the housings, hooked everything back up as it was, and I still don't have reverse lights. I checked the harness, replaced a bunch of worn and falling apart butt connectors with solder so I know the connections are solid from the previous owner all the way back to what is obviously stock harness. I believe all of the shotty work has been removed and cleared out.

    My tail lights are now better than ever before. I am still however not got any reverse lights. the circuit they look to be attached to is putting out .032V with the key on and the truck parked in reverse, and the bulbs are brand new and tested good. I assume it is possible that the switch has failed, but getting at it is the trick. is it accessible without taking the cab off? is that circuit accessible from in the cabin that I could use a DMM and test it to see that it is/isn't working. is is possible to borrow that signal from another circuit and i could make my own Relay setup to click them on. This old girl has a lot of miles on her, but before I rig up a switch and turn the lights on myself when going into reverse, I was hoping someone could point me in the right direction.

    PS This is my first post here Thanks for the add, found this forum googling my issue.
  2. Dino soar

    Dino soar Road Train Member

    Dec 8, 2017
    First thing I would say is make sure that you have a good ground to that reverse light, preferably running a separate ground to it and see if that helps. So many crazy issues with lights happen because of a bad ground. Use your multimeter and test for electricity at the pigtail.

    You should be able to go to the top of the transmission and that switch bolts into there. You should be able to test it with a multimeter and even run your own lines out of there and connect your own bulb but the multimeter will tell you if the switch is working and if it has electricity, Etc. You could have a blown fuse or something that's not sending electricity down to the switch.

    But the switch itself is pretty simple. The hot wire goes to one side and when you put it into reverse the switch closes and electricity flows from the other side and runs your grounded light.
  3. flipper66

    flipper66 Bobtail Member

    Jun 19, 2019
    The reverse light shares a common ground with the brake lights, and is bolted on(I bought cheap generic trailer lights at the auto parts store as they are simple and get the job done). we also wire brushed to bare metal before bolting it down. I'm very confident that the ground is good, I've worked on enough old cars to know how much of a pain that can be. I have also used the brake light lead and swapped that to the reverse pin and the bulb illuminates properly.

    I looked at the fuse box, but didn't see any fuses listed as reverse or anything close. is it on another circuit?

    I figured the switch was pretty simple, this isn't a modern truck with all kinds of sensors on it anyways, and most everything is serviceable very simply. Just got to get down there and try and figure out which one it is.
  4. Working2party

    Working2party Medium Load Member

    Feb 10, 2018
    A lot of times they use the same power for the air dryer heater. The breaker may be marked for that.

    I’ve also seen to may times that the wires get switched around on the reverse switch.

    No exactly sure about your truck, but usually you can pull the center carpet or mat loose and have a 2’X3’ plate you can remove to really open up access to the top of the tranny.
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