Namely, whoever put the hydra-bed on our duramax. They cut the harness to the box when they pulled it, and wired all the lights (6 s/t/t and 4 marker lights) into the trailer plug. Plug in a trailer with the factory rated fuse in the box, and they blow within 5 minutes, both the signal/brake and tail/marker fuses. Changed a tire the other day and found that the power cable to the hydraulic pump is about three feet too long, and was laying across the muffler. It arced enough that half the conductor is gone. Lucky there is any electrical system left at all.

There is some sort of electrical box on the rear crossmember with two harnesses plugged in, with room for two more. Any idea what else would plug in there?

 

Like you said, you need to hire an electrician.

 

Bummer, I hate hacked wiring (as an electrician!). If you feel comfortable with wiring you can do it yourself, if you can find the original harness somewere (junkyard?) and replace it to where it's been chopped out, with some good soldered splices and weatherproof heatshrink. Then wire just the tail/stop/turn lights to the original harness, add a relay (or probably two, one each side) and seperate feeds to additional marker lights to keep any extra load off the original wiring. Biggest thing is to keep everything protected by correct sizes fuses, which from factory almost all vehicles can use a fairly high rating compared to the wire size, which is why it's important to not add too much to it, or something will burn up eventually (usually a connector). Good grounds are a must, I don't use anything less then 12 gauge wiring to the rear of a vehicle because of the distance from the battery for voltage drop, and I try to solder anything that won't need to be regularly removed (like lights). Good luck.

 

This thing was installed in town somewhere. I need to crawl under it and wire the bed lights into the original factory bed harness. It was cut off with about 3 inches of wire coming out of the connector, so I can do it without too much trouble. Might be able to go out back and pull a tail light out of the original box to check the wire colors.

I've done a bunch of wiring repairs, even gutted and completely re-wired a trailer myself, but I hate having to fix other people's screw-ups. They tied into the harness to the original 7-way plug, and wired a 6-way and the bed off that splice. I stepped up one size on the trailer fuses to keep things working, but need to get this fixed. Need to find some time first, seems like that's one thing we never have enough of to get to things like this.

They probably never thought about the extra load on the circuit, or never thought that it would actually have working trailer lights plugged into to.