Trailer wiring question - I'm stumped...

[dx3]

Guys,

My friend recently bought a boat. The trailer it came with is pretty old, so I set about replacing the wiring harness and all the lights for him (he's not the most technically inclined). So we have a completely new harness, new lights with all new bulbs. All grounds are good.

He has a 4-wire connection coming out of his truck, into a 4-pin plug for the trailer. 4-pin plug has also been replaced.

So basically this is what we are working with:

Well, I cannot get the turn signals to work. Everything else works fine. The truck turn signals work, and I replaced the bulbs for the turn signals on the trailer and still no luck. What confuses me is that the turn signals work, but the brake lights don't, even though they are running on the same wire (thus it is getting power.)

So when everything has been replaced, all grounds are good, what is my next step? Should I be getting 12v out of the plug when the brakes are on out of either the green or yellow wire pin? I would have thought so, because I do when the turn signals are on... However, when the brakes are pressed I still get 0v.

The only other thing left to do is to splice into the brake harness on the actual truck and run that through a 5-4 pin converter... But, that's like giving up! Any ideas?

 

[farmerbyron]

Sounds like the problem is on the truck side. Check fuses.

 

[peanut]

Sometimes the hitch is a contact/ ground! Did u set the hitch on the ball and try it?

 

[Larry Morgan]

Start eliminating variables. First thing I would do is get a simple test light or a multi-meter and check what's happening at the plug itself. Make sure the truck is actually providing power when the brakes are applied and turn signals are turned on. As farberbyron said, this sounds like the truck's issue. I have actually encountered this problem before, but the problem was never tracked down due to it not being my truck.

If you find that the truck in fact isn't giving power to the trailer, check all the fuses (if you haven't already). If none are bad, you may have to trace the wiring down for the trailer harness. Because of the way the trailer is wired, it's essentially impossible for it to be at fault, if you can get both lights to come on using turn signals like you said.

 

[DanB]

Get a test light and check the plug on the truck. Rule that out. Have him hit the brakes, then R & L turn signals. If they all check out then move to the trailer.

 

[dx3]

Thank you all for your responses. To answer some questions:

What fuse would you check that would only stop trailer brake lights from working? There is no in-line fuse for the truck harness, and if the brake lights work on the truck, then I can't imagine there being any specific fuse.

I did not set the trailer on the hitch, but if everything else worked, don't you think there are sufficient grounds? Additionally, the white wire is a ground.

As mentioned above, I do get 12v at the plug when the turn signals flash, but I don't ever get anything at the plug when just the brakes are pressed. Which would lead me to believe the trailer is fine and the truck is the issue.

Again, thank you for everyone's responses. Also, I am not being argumentative, rather trying to play devil's advocate Thanks again guys,

Jonny

 

[peanut]

Thank you all for your responses. To answer some questions:

I did not set the trailer on the hitch, but if everything else worked, don't you think there are sufficient grounds? Additionally, the white wire is a ground.

Again, thank you for everyone's responses. Also, I am not being argumentative, rather trying to play devil's advocate Thanks again guys,

Jonny

Try that and it is and it is easy to eliminate! I had a flat 4 connector that did the same to me and just drove me nuts untill i hooked up the trailer and all of sudden everything worked. Hey, IDK!!
Tim

 

[dx3]

Try that and it is and it is easy to eliminate! I had a flat 4 connector that did the same to me and just drove me nuts untill i hooked up the trailer and all of sudden everything worked. Hey, IDK!!
Tim

Tim,

Certainly willing to give it a shot at this stage Thanks again,
Jonny

 

[peanut]

No problem.
BTW! i think I am about to inherit the car, which I am actually looking forward to! Lol!
Wife is wanting a new one!
I think i saw you in BA a couple weeks ago between 61st and 71st on Elm.
Nice advertisement by the way!

 

[farmerbyron]

Thank you all for your responses. To answer some questions:

What fuse would you check that would only stop trailer brake lights from working? There is no in-line fuse for the truck harness, and if the brake lights work on the truck, then I can't imagine there being any specific fuse.

I did not set the trailer on the hitch, but if everything else worked, don't you think there are sufficient grounds? Additionally, the white wire is a ground.

As mentioned above, I do get 12v at the plug when the turn signals flash, but I don't ever get anything at the plug when just the brakes are pressed. Which would lead me to believe the trailer is fine and the truck is the issue.

Again, thank you for everyone's responses. Also, I am not being argumentative, rather trying to play devil's advocate Thanks again guys,

Jonny

Usually there will be a separate fuse for trailer brake lights. That way if you hook up to a trailer and it shorts out, you will still have lights on your truck. Check the owners manual to locate this fuse.