Power to trailer lights, but no lights?

Hey guys.
So I just bought this truck. I went to tow a small trailer, and no lights. So the other day I went at it with a volt meter and tested it with the flashers on. The odd connector is the ground, and I tested the other three wires. Every time the lights blinked the voltage went up, so I cleaned all of the connectors and tried again. Still no lights at all? no running, signal, or brake lights. What could be wrong here?
Thanks guys!

 

Is the plug good on the trailer? Did you check voltage after the plug?

 

Ground on the trailer? Check the wiring on the trailer.

 

First off, is it an OEM harness on the truck or an aftermarket? The quick things to check are on the trailer itself. Check to see if there is oxidation at the bulb connections and check the grounds. Move the wires around with it plugged in to see if you get lights because it could be a broken wire somewhere in the line. Have fun chasing the gremlins. I recently rewired mine and went with LED and soldered/heat shrink wrapped any connector that I could. Hated replacing bulbs/housings.

 

And do you use the circular connector or the adapter? I had an adapter with a bad left light contact. Check voltage further down the line. A cheap test light with a really sharp probe can pierce insulation and test a lot quicker than a multimeter.

 

All of the plugs are good on the trailer, I've tested it on two separate trailers. both of which were used within the last week with other vehicles and worked fine. So I know it isn't the trailers that are the issue.
I am using a 4 prong connector, and I am almost certain it is a factory harness because it connects into the factory harness up above (no splicing, etc. either). I just don't see how it could be an issue with the harness or anything before it if I am getting voltage at the connector on the truck.
I am pretty stumped. Are there other parts that control whether or not it would be putting enough power to light the lights or anything?

 

I just went through that with my trailer and I found a kit at Walmart with two lights(super cheap) two small amber marker lights 25 feet of 4 strand wire and a plug for $24 so I literally ripped everything off and just started over. Too many time I spend time finding the problem just I fix it and have another pop up somewhere else haha

 

What was the voltage at the plug?

 

This...check after the adapter...perhaps your adapter is bad...

 

Turn your headlights on when hooked up to the trailer. Then everything will work fine. Seriously. I had the same problem. It's a quirk of our towing package.

 

Yeah redoing the trailer lights wouldn't make a difference because they work on other vehicles. I am not sure what the voltage was because it would not really read it because it was so quick on and off. But the few times that I did see it, it was around 12 volts. I did try the lights with my lights on because I wanted to see if the running lights would at least work. But nothing. I am just confused.

Could this be the issue? Is there any way that the little box could have had something go bad in it?
http://www.napaonline.com/Catalog/C...-Tow-Vehicle-Custom/_/R-BK_7551589_0249738225

Thanks for all the input, I really appreciate it!

 

What were you grounding the multimeter to? The truck or the ground pin on the harness? If you used the truck, then it's the ground of the harness that's your problem. If you used the pin of the harness then I'm stumped because if you have power coming back to rear of the truck, and a good solid ground making it back to the frame then there is nothing else it can be. Do you have a brake controller installed?

 

Don't check the plug with the blinkers on, just check it with the lights on. Also check it to the plug ground, not just any place. You want to make sure you have a good ground in the plug.

If you have voltage at the plug, then check voltage at each bulb socket on the trailer. If no voltage in the sockets then try your adapter. Ring it out with a continuity tester to see if the wires are broken.

 

Oh yeah I've been checking with the ground on the adapter. Maybe I'll see if I'm getting anything to the bulbs at all. And I'll check with just the lights on and see what I get. Maybe I'll check with grounding to the frame and see if I get different results too.
Hopefully I can corner the issue soon.
Thanks for all the input!

 

So I bought a trailer light tester kit and tested the connections on my truck. It basically plugs into my 4 prong connector and has lights that light up when they get power. I flipped the lights on and the running lights light came on on the tester. Left blinker, light came on. Right blinker, light came on. Flashers, both blinkers came on. All while the running lights light stayed on on the tester.
So I thought hey, lets try it again! Plugged into a trailer, and nothing. I am just stumped. I'll try another trailer tonight and see, and test after the wires with the probe that it came with. I just don't understand why none of the trailers I have tried have worked. Does the trailer need to ground out to the truck through the hitch and maybe there is an issue with that?
Thanks guys.

 

As long as the grounds go back through the connector it should work. You should also test the continuity on the ground in your plug. One test lead to the ground in the plug, and one lead to a bare metal part of the truck. If no continuity, then the ground is bad in the wiring harness.

Also test with a meter right at the light sockets and see what voltage you get.

 

That could actually be it. I'll have to give that a try!
Thanks!

 

If the ground was no good on his truck, then the plug tester he spoke of would not have worked.

Edit: All indicators point to the trailer.

 

He had tried other trailers that didn't work, which indicates that the truck harness may not be good. This is why testing in sequence, easiest to hardest, is recommended.

 

Alright, thanks for all your help guys! I think I've got the problem dialed.
I played with all of the connections on the truck and tested everything as stated above. everything looked fine. I tried on the trailer again, and I finally got something to work!
Flipped the lights on, and hazards, and hooked the trailer to the hitch to make sure it wasn't some weird ground to the truck thing or something. At first the lights did nothing, but I found that if I hold the connector in a certain way then it gets connection and finally works.
I think the trailer had some issues though, because I couldn't get the right blinker to do anything. Probably the bulb on the trailer out or something.
So I am going to get a new 4 prong connector from walmart and splice it in and try that. I am almost certain that it is just the truck's connector having a short inside, as well as the fact that the ground prong is cracked at the base. I'm going to give that a try and see what happens from there.
Thanks for all of your help!