Trailer light problems

[MBJJ2369]

I am having some big problems with my trailer lights. I have a 4 pin plugged into a 7 pin adapter. When using a test light I have power to the tail lights and power to the turn signal. When I put in the bulb the it doesnt come on. I have used 4 different bulbs. I also happened to touch my test light probe to the trailer frame and the light in the tester came on. Any ideas would be greatly appreciated.

 

[4now04]

Make sure you have good ground connections. The white wire in the harnessis the ground. You might try using a temporary jumper wire between the vehicle and trailer, or from the vehicle to the ground connection on each light.

 

[GA_Boater]

I also happened to touch my test light probe to the trailer frame and the light in the tester came on.

Don't quite understand this. Are you saying with the test light wire on ground and touching the probe to the frame that the test light came on?

 

[MBJJ2369]

Yes sir, I had it grounded to the frame and then touched the probe to the frame and the test probe light came on bright and strong

 

[MBJJ2369]

Since I have to leave bright and early in the morning, I did a quick rewire job. I will redo it all again this weekend.

 

[ahicks]

This would indicate the ground circuit (white wire) is not making it to the trailer. Sometimes you can get away with a quick fix using a piece of steel wool. Set it on top of the ball, then set the coupler down of top of that.

 

[M2HB]

I wire all my trailers basically the same. I never use a 4 pin plug even if I only need 4 wires. I hate those adapters. I purchase 7 conductor wire, knowing I won't use the brakes (blue) wire. When wiring a trailer with no brakes, I buy the 14ga 7 conductor wire. With brakes, I buy the heavier 12ga wire for the brakes. I wire the 7 conductor wire to the 7 conductor RV plug and then run the wire all the way back to the first connection which is usually the back of the tongue where the first clearance light it. If there is no place to run the wire, I use 3/4" EMT conduit.

It makes for a nice job and it eliminates many of the problems people usually run in to.

 

[Sprig]

In general I’ll say most of the trailer wiring problems I’ve seen have been due to a ground problem. I always check out the grounding first. Also always have the trailer on the hitch ball when wiring and trouble shooting. I’ve seen a number of cases where the lights wouldn’t work unless the trailer was hitched to the vehicle.

 

[GA_Boater]

In general I’ll say most of the trailer wiring problems I’ve seen have been due to a ground problem. I always check out the grounding first. Also always have the trailer on the hitch ball when wiring and trouble shooting. I’ve seen a number of cases where the lights wouldn’t work unless the trailer was hitched to the vehicle.

And that's called a bad ground.

The ball can't be used to supply ground to the trailer or we wouldn't have the white wire to connect the trailer and TV frames.

If you like flickering or non-working lights, use the ball.

 

[QBhoy]

Could always grab a meter and test for continuity at each end.
Other than that and broken wires...only trouble I have seen with trailer lights, is with LED lights not working with modern vehicles. The can bus system throws it all to **** making the lights go crazy.

 

[ahicks]

He's actually done one of the quickest down and dirty tests to check trailer ground. With the lights hooked up, turn on one of the turn signals. Then hook one end of the test light to a good ground on the tow vehicle (chrome bumper works great. Then take the other end and poke the trailer frame with it. If it's flashing, you have a bad ground - no if's to it!

 

[GA_Boater]

Yes sir, I had it grounded to the frame and then touched the probe to the frame and the test probe light came on bright and strong

We don't what frame he's talking about. I have the impression he grounded the test light to the trailer and touched the probe to the trailer frame. :noidea:

 

[ahicks]

The light did come on. If the test leads were attached as you suggest, that would not be possible, in any circumstances.

 

[GA_Boater]

The light did come on. If the test leads were attached as you suggest, that would not be possible, in any circumstances.

I agree. So the OP needs to explain.

 

[Sprig]

In general I’ll say most of the trailer wiring problems I’ve seen have been due to a ground problem. I always check out the grounding first. Also always have the trailer on the hitch ball when wiring and trouble shooting. I’ve seen a number of cases where the lights wouldn’t work unless the trailer was hitched to the vehicle.

I should have been a little clearer. I always hook the trailer to the tow vehicle when wiring, rewiring or trouble. That creates a super ground. Once I see that all the lights and bulbs work I disconnect the trailer from the vehicle and check the light functions. If the6 still work you’re good, if they don’t you know it’s a ground problem.

 

[MBJJ2369]

I attached the grounding lead of the test light to the boat trailer and touched the probe to the trailer and the light came on in the test probe. The only time it would not come on was if I touched the trailer with the probe within 4 inches of where i had it grounded.