Backup alarm/backup lights issue

@Goodysnap

 

I have not seen this exact problem yet. The reveres switch is normally open and closes contacts when reverse is engaged. You likely have an intermittent short to power on the reverse circuit somewhere on the chassis.

 

Maybe try a jumper wire from reverse switch to backup alarm and disconnect the original power going to alarm and make sure there’s good contact for ground. This would eliminate any bad wire between reverse switch and alarm. I just had trouble with a bad ground for backup alarm and lights and it causing different issues with backup lights and alarm.

 

Anything is possible.

Acts up when wet tells me it’s wiring outside the cab. Water makes the short happen more where the wires are touching.

 

You may have a chassis module that sitting on the frame outside the cab.

If you have a problem with water getting into the connector, then this would be the cause.

 

If it has a Chassis Node then A8 is the back-up input, C21 is the back-up alarm output. Pull off the three 21 pin connectors from the node and check for corrosion and or moisture. (Update: 567 does have a Chassis Control Module, about mid 2019 looks like it changed from a 3 to a 5 plug node. Vanderhaags has used for $650. New is about $1,600. I would make sure wiring is good first) Really need a wiring diagram and a multimeter. Without a diagram trace the wires from the tail-lights forward. There should be a connector between the tail-light harness and the rear chassis harness. Then trace the wires from that connector forward to the next connection. Find the hot wire for the back up with the truck in reverse. Then check voltage at each connection. Check ohms on each harness(es) for the hot wire, key off no power. With the truck in neutral and key on you could try to move the connections and wires to see if the alarm will come on.