RedOne

Check for voltage at the plug. I believe the ignition switch has to be on to have voltage at the pin for lights and charging of the battery. Is it 4, 5 or 7 pin plug?

benchwarmer4203

If all of the relays and fuses are installed, get yourself a voltmeter (you can get a cheap one for ~$10 if you don't already have one) and check for voltage between pin 5 and pin 2 on your 7 pin RV plug with your truck running, or at least with the key in the "on" position. Pin 5 is the top right pin, and pin 2 is the bottom left pin (voltage should be between 12-14V.) That'll tell you if there's charging voltage for your trailer battery. Also check the voltage on the trailer battery (I'm assuming it should probably be between 12-14V as well.)

This is assuming your 7 pin wiring is the same as mine, of course. Let us know what you find and we'll keep helping you troubleshoot.

Abn150

^^ Good info above, although I believe 1 & 4 are the correct pins, top left and bottom right, as you are looking at the truck. Here's a pic to make it clearer. The wiring should be standard to this schematic.

Abn150

One suggestion before you get into a lot of troubleshooting, sometimes using process of elimination can help to direct your troubleshoouig efforts.

If you have someone with another truck you can borrow, hook your trailer up to that. If the interior lights work, then you know that the problem is in your truck wiring. If the lights don't work, then the problem is in your trailer wiring.

benchwarmer4203

I must have pulled the wiring for a different truck when I found the diagram on the interweb. My apologies. If you're still having problems, another thing you can verify is that your pigtail from the trailer actually matches up with the wiring on your truck.

Funny story about that...I was pulling a small test trailer for work a few years ago with my personal truck. We hooked up the trailer, made sure all of the lights functioned, and off we went. A couple hours later when we got to the station I went to back the trailer into position and the thing was fighting me the whole time (I thought it was just my inexperience backing trailers at first.) Then I realized that it wasn't just hard to turn, it was hard to move in general. The trailer brakes locked up when I put the truck in reverse. I hadn't noticed the lack of trailer brake on the haul because the trailer was fairly light (less than 2000lbs.) Turns out, the trailer was wired for our company trucks, and our company trucks had the pin for the trailer brake and the pin for the reverse lights switched. That meant when I put my truck in reverse I was sending full voltage to the trailer brakes, haha. No harm no foul, we actually rewired the trailer after that, haha.

RedOne

That is what the 5 pin plugs are for (locks out brakes while backing up and backup lights if installed) plus a ground, running lights, turn signals and brake lights. The 4 pin plug is for surge or no brakes on trailer and the 7 pin plug is for all the above with the brake controller and charging battery/aux lighting system in trailer but only while key is "ON". That way a trailer will not kill the truck battery if you leave a light or something on in the trailer.

benchwarmer4203

Yeah, this was 7 pin...talking with the mechanics after the fact they told me they rewired all of their trucks and trailers to a company standard that was intentionally different than the OEM standard. No one bothered to tell me that, though. They just knew I had a truck and told me to pull the trailer.

Abn150

Why would they do that? So you would wreck thier trailer if you tried to steal it?

benchwarmer4203

That was always my guess; but I could never get a good answer. I told them after that first haul that I wouldn't tow it anymore unless it was rewired for my truck.

Stefanieb

Thanks all, I will see what I can find out and let you know!