Trailer wiring

[thartiga]

Rewiring trailer and having issues. Installed new wire connector with junction box that made the wiring real clean and easy. Problem is only getting 8 volts at the junction box with the lights on. I get 12v with no load. If I run a ground wire from the junction box to truck I go back to 12v.

I've hooked the truck up to other trailers with no issues. So, I think it is between the connector and junction box.

Any other ideas? The plug is molded with the wire as I thought this was going to eliminate issues.

Tim

 

[John B.]

I've never used a volt meter to check trailer wiring, always used a test light. Do your trailer lights work at all??
If you run a ground wire to your truck and get good results, then I would use a ground wire to the truck. I always run a
ground thru my trailer plug to the truck frame and then to each light so I know they get a good ground.
I make trailer wiring and checking much easier when I use a battery charger on each circuit. I'm even going to put trailer
plugs on my battery charger with a toggle switch wired into each circuit.
But the final test is when it's hooked up to the vehicle. Wiring a trailer is one of the most simple electric projects a
person can do.

 

[VicS]

Did you run a ground to the trailer frame
to the ground wire in your box. Did you
spray cleaner on your plug? I have found
soldering and heat shrink tubing best.
Then yellow and red twisters,wire nuts for
120v second.

 

[thartiga]

This is a 7 way round plug from truck to trailer.

I put a nice ground from the j. Box to trailer. I also have the ground going to the brakes and lights.

What gets me is our other trailers work fine with this truck.

 

[Jim in Ma.]

Any time I have had a trailer light problem - Most often it has been a ground problem.
Go back over your steps starting with the ground connections, then move on.

 

[RustyS]

Jim has it right. If you adding a ground to the truck brings the voltage up to 12v, you need to fix a ground connection somewhere. I would go so far as to find the ground wire behind the plug on your truck and splice in a wire to the truck frame. If it is a tilt trailer run a ground from the tilt frame to the trailer frame.

 

[DENNIS MIN]

RustyS,

When I had issues, I took a jumper cable set, both the black and red on one end of the jumper were hooked directly to the battery negative (ground). One the other end of the jumper, I clamp one to the truck frame, the other to the trailer frame...then see what I had.

Essentially what you said.

D>

 

[thartiga]

It was a ground issue. Hooked the trailer to another truck and worked fine. Was a bad connection in the connector in the truck. Purchased new and is good. No idea why it worked fine with other trailers.

Thanks for the help.

 

[4play]

So the ground wire was bad, the only other place a trailer can ground to the truck is through the ball or hitch. If the hitch is not hooked up, rusty or corroded then the trailer will not make a good ground or any at all, you should never rely on the hitch for a ground path though. Maybe those other trailers you checked had a better connection through the hitch, possibly from being used more frequently or that you hooked it up to move it for testing.

I used to borrow a trailer from a friend of mine and always checked lights before I left. I usually had to move the trailer a few feet and make a turn or two before the lights started working, doing this was cleaning the ball/hitch to make a good connection. I eventually fixed the wiring on the trailer. If you see a trailer going down the road with flickering lights, its probably got a bad ground and losing the connection through the ball when hitting bumps.

 

[john *.?-!.* cub owner]

(quoted from post at 18:43:27 01/22/16)
It was a ground issue. Hooked the trailer to another truck and worked fine. Was a bad connection in the connector in the truck. Purchased new and is good. No idea why it worked fine with other trailers.

Thanks for the help.

he other trailers were probably grounding through the ball, and the one were rewiring was rusty inside the hitch, or not setting on it tight.

 

[RustyS]

In the late eighties to early nineties Chevy had an issue with a ground on the tail light plugs. The poor ground would not let enough current pass across the bimetallic strip that operated the blinkers causing the light to blink rapidly. When a trailer was hooked up the added load and extra current draw would cause the blinkers to operate properly. Funny how I can remember that but have no idea where I left my half inch ratcheting wrench

 

[IA Roy]

I have ran a separate ground wire from the negative battery cable directly to the trailer plug. The most positive ground I could think of.