Chad_Mack7

Well, I finally figured it out. Double checked the ground and re-did it to be sure it was well grounded. No change. I tore the whole dash and wiring harness apart basically, tracing wires from the switches to the harness and trying to find any issues. Then I found a junction box at the back of the truck where truck harness wires came in and then were disbursed to the appropriate lights. Well, the wires I'd been chasing (the factory wires) weren't even connected anymore. Instead, I found a newer set of wires running into the box and connected to the appropriate connections. Someone re-wired the lights at some point!! Very carefully traced the new wires and found that right between the two drive axles, the wires were hanging down and hitting the drive shaft. All the wires except the reverse wire were completely cut through... Thanks a lot previous owner! Anyways, did a legitimate splice job, covered wires well, rerouted them to a safer location, and all is functioning as it should! I appreciate the help!!

Good point! There wouldn't be a separate fuse or relay for just the back lights or something? I'll double check everything tomorrow and see what I find!

I traced them all up to the cab and it seems to just go into the cab with no connector. I'll have to double check, but pretty sure it all ran without connectors. Or maybe they ran wires into the cab and did the connection under the dash?

So I have a 1999 mack mr688s that has a concrete boom pump mounted on it. All of the park lights, brake lights, and blinkers quit working pretty much at the same time. 2 lights on either side going down the truck and everything on the back. I've been chasing wires and found nothing. I can't find or don't know of any diagram for relays or fuses. Everything on the cab works great. Clearance lights, front park lights, headlights and front/side of cab blinkers all work great, just everything from the cab back isn't working. Anyone have any ideas??