Trailer guys, wiring problems

[Moparracer89]

Long story short, last trip with my trailer the plug housing on the truck cracked, allowing the plug to fall out and drag pretty much destroying it. New plug on truck and trailer side.

Pulled my trailer out today to go to the dragstrip and the lights and brakes are all messed up. I pulled both plug ends apart and verified all the wires/colors match up on both plugs. What happens is, when I plug in the trailer, the running lights come on. If I turn on the headlights, the running lights turn off (opposite of what should happen). The brake controller also isnt seeing a trailer attached and Im getting zero amperage output to the trailer brakes.

With the trailer unplugged, the truck side plug checks out fine with a volt meter. Each connector has voltage when it is suppose to. Plug in the trailer and the running lights and turn signals show 0.25 volts, should be zero. I thought maybe the breakaway battery was backfeeding, but disconnected it and same problem.

Thoughts before I rewire this entire thing? Also, every connection on it is made with those cheap push together type splice things.

 

[1911ly]

Bad/missing ground at the plug or at the lights. Run a ground wire from the frame on the vehicle and touch it to the trailer grounds at the different points. You will find it. A good test light would help, or a voltmeter. I prefer a test light for an easy visualization of the issue.

 

[Grump01]

Years ago was trying to help a FIL wire a vehicle to a trailer. Similar problems as yours and was redoing the vehicle etc and couldn't get things correct. Turned out the plugs were the molded rubber type and one half had a short within the plug. Changed plug and put wiring back to where it was to start with and everything worked then. Best of Luck. It can be frustrating.

 

[long coat]

The color code may not be the same for the truck and trailer.
Green on the truck might be right turn and it may be Trail on the trailer.
You need to check function on each and put in the right spot.

 

[eldirector]

I just had to replace the plug on my trailer as well. I'll concur with the two main thoughts above:
1) Check your ground. I'd almost lay good money on this being the issue.
2) Check the position and function of each wire independently. Colors can be misleading.

I'll also add, since you said the connector drug on the ground for a while, to check for shorts and broken wires in the pigtail. All the way back to the frame.

IMHO: trailer wiring is crap on a good day.

 

[Moparracer89]

The plug wiring is correct. I pulled both sides apart and verified each wire connects to its mate on the other plug correctly. The trailer side plug never had a ground in it, so I assume the trailer is grounded to the frame somewhere, just have to find it. And then run a clean ground to the plug.

 

[Gary119]

6 way or 7 way plug? 4 way doesn't have brake wire. Is plug on truck a factory plug? Year of truck?

 

[Gary119]

Something worth noting. If you look at your truck plug (standing behind the truck looking forward) look at the wires clockwise. Turn around and look at the trailer plug the wires will be counterclockwise.

 

[long coat]

The plug wiring is correct. I pulled both sides apart and verified each wire connects to its mate on the other plug correctly. The trailer side plug never had a ground in it, so I assume the trailer is grounded to the frame somewhere, just have to find it. And then run a clean ground to the plug.

Why do you think the trailer plug never had a ground?

 

[eldirector]

The trailer plug never had a ground wire? It was expected to ground through the rusty, greasy (and painted) hitch? I'm surprised it worked very well before.

On that note, were you actually hitched up when you tested? Or, just plugging in the wires? If NOT hitched, and no ground wire, then the noted behavior doesn't surprise me one bit.

 

[NavyVet]

I believe there are a couple different wiring standards for the 7 pin connectors. Either way, I would check it with a tester (or meter). U-haul used to sell a plug that had lights/leds built-in so you could see as each wire activated.

Regardless, I have not seen a specification that didn't pass a wired ground through the connector. None of them should just rely on chassis contact through the hitch... Specially dangerous if you are running electric trailer brakes. That is an accident waiting to happen...

 

[Moparracer89]

Why do you think the trailer plug never had a ground?

Because as I said, I pulled the trailer plug apart and there is no ground wire. Its just grounded through the chassis.

 

[Moparracer89]

6 way or 7 way plug? 4 way doesn't have brake wire. Is plug on truck a factory plug? Year of truck?

7 pin. 04 Dodge Ram had a factory 4 pin.

 

[Moparracer89]

I believe there are a couple different wiring standards for the 7 pin connectors. Either way, I would check it with a tester (or meter). U-haul used to sell a plug that had lights/leds built-in so you could see as each wire activated.

Regardless, I have not seen a specification that didn't pass a wired ground through the connector. None of them should just rely on chassis contact through the hitch... Specially dangerous if you are running electric trailer brakes. That is an accident waiting to happen...

It appears that that is how this was done. I never gave it a thought before because it worked fine.

 

[long coat]

If it was a factory plug, it had a ground. I think Dodge used a black wire for ground.

Dodge has their own wiring color code & it changed every year for a few years.

 

[Gary119]

All late model 7way plugs are the same/standardized. Start at top going clockwise. Top positive battery......right turn/stop.....electric brakes..... negative battery.....left turn/stop.....running lamps.....round center is backups. This is standing a rear of truck looking forward.

The "had a 4" is concerning. It isn't one of them "adapters" where you plug a 4 way into the back of a 7 way is it.

Or is it someone cut off the four and only connected 4 of the 7?

Ground can be black or white.

Picture?

 

[long coat]

Dodge for what ever reason had the flat 4 just hanging, most of the time it was up under the bumper and people didn't even know it was there.

 

[Moparracer89]

All late model 7way plugs are the same/standardized. Start at top going clockwise. Top positive battery......right turn/stop.....electric brakes..... negative battery.....left turn/stop.....running lamps.....round center is backups. This is standing a rear of truck looking forward.

The "had a 4" is concerning. It isn't one of them "adapters" where you plug a 4 way into the back of a 7 way is it.

Or is it someone cut off the four and only connected 4 of the 7?

Ground can be black or white.

Picture?

I converted the 4 to 7 pin on the truck myself. It has a ground, the trailer does not.

 

[long coat]

What's the trailer?
Was a wire on the spot marked "white" in the plug?

 

[femurphy77]

Something worth noting. If you look at your truck plug (standing behind the truck looking forward) look at the wires clockwise. Turn around and look at the trailer plug the wires will be counterclockwise.

Made this mistake on two occasions; one of them for 950 miles! I still don't know how it didn't fry the trailer brakes.