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Need some help with trailer wiring.

black rust

black rust

1/2 ton status
Joined
Jun 29, 2007
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Location
Beecher, IL
Tomorrow I'm going up to Badlands for a quad trip, and my DD Explorer is being used to tow the trailer. Lucky me, my trailer lights refuse to work. I know the problem is on the vehicle end, trailer checked out fine. I checked the fuse, it was good. Checked the wiring all the way from the fuse box to the 4 pin plug, it all looks good, with no pinches or breaks. I checked the relays, they seemed good. Any guesses as to what is wrong, because I've exhausted all ideas.
 
How does the pulg look? Is it all coroded(sp)? What about the ground? 90% of the time trailer light problems are in the grounds. Have you taken a test light and tested the plug to see if you getting power through it?
 
Plug was just replaced a few months ago. I've been putting tester leads into the plug and checking for voltage as my way of testing if I was successful. As for the ground, I also tried sticking one of the tester leads on the hitch to ground it, and got the same results.

Edit: just went back out there and tried again. I was getting anywhere from 0.00 to 0.03V, with or without the lead grounded, which I'm guessing is just a minor inaccuracy with my tester, but I figured I'd mention it.
 
Get yourself a test light. Find a good ground for it and have someone run the light controls in the vehicle while you probe the plug on the vehicle side. Another thing to check is where the plug is added to the vehicle factory wiring, make real sure that there isn't any kind of corrosion there or it will cause problems. Also, take the ground off and clean it extra good.
 
Well, I just ran a jumper from the battery negative to the back to use as a ground and got nothing (except 0.08 to the other ground). Ran it from the positive to the ground on the plug and 11.5x volts, so it is at least partially working. I can try a test light, but right now it looks like I'm not getting power at all. Also, I checked the both plugs on the factory harness when I replaced the end plug, and cleaned them up and put some dielectric grease on them, so they should be good.
 
black rust said:
Plug was just replaced a few months ago. I've been putting tester leads into the plug and checking for voltage as my way of testing if I was successful. As for the ground, I also tried sticking one of the tester leads on the hitch to ground it, and got the same results.

Edit: just went back out there and tried again. I was getting anywhere from 0.00 to 0.03V, with or without the lead grounded, which I'm guessing is just a minor inaccuracy with my tester, but I figured I'd mention it.
Click to expand...

Takes 12 volts to make the lights work. Check further back where this trailer wiring connects to the vehicle wiring like someone already said.
 
If your vehicle is getting the normal lights (turn, park, brake) but your trailer plug is not, then its in the plug/pigtail/connection or ground.
 
I disconnected the harness at the plug right before it enters the vehicle. On two of the pins, I got 0.02 and 0.05 V, with the other lead grounded to the battery. Is it possibly for relays to fail in a way that only lets a small amount of voltage through, and still tests out okay?
 
With the trailer plug connected to the factory vehicle wiring harness at the back of the vehicle, does your vehicle taillights work properly?
 
The taillights work fine both ways. The is the four pin plug at the end, that plugs into a plug on the passenger side right above the hitch. that one runs right under the driver-side taillight, where there is another plug. This one runs up into the taillight housing, where it goes together with the taillight, reverse light, and blinker, and goes into the body through a grommet. So, all trailer wiring is after the taillights, and on completely seperate wires.
 
The trailer pigtail harness should be connected to the vehicle factory harness before the wires split to each of the truck taillight housings. Is this how yours is?
 
Yes, the wires all run along the length of the truck to the fuse panel in the dash, where they combine and go to the proper fuses. I just checked every single fuse, they are all good. I also just found out my license plate lights on the rear aren't working, and those wires are grouped with the trailer wiring.

Also, my power windows don't work, but I can get them to work by messing with some vaccuum operated canister with a metal rod coming out of it. I'm guessing it isn't related though, because even when I can get the windows to work, the trailer wiring doesn't work.
 
That's whats confusing me here. Right now, I'm testing from the plug right before it goes into the body, with no other breaks that I can find before the fuse box. I'm also running a wire to the negative battery post to make sure I'm getting a good ground, and I still only get very small readings. I also tried my old trailer plug, and still got the same results
 
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