trailer 7 pin plug

[murph1068]

So all of a sudden I lost my right turn signal and brake light on my trailer. I still had running lights and left signal but parked it and no time to check it out. Today I hook it back up to the truck and I have zero....nothing. I checked the truck pins and I have power to the outlet on the bumper so I suspect the plug on the trailer is the culprit.

I see the center pin is not there nor the pin for the positive terminal. My question is... Does the trailer use all 7 pins? I can't even see in the slot to see if the blades broke off in there. Is this a common problem?

 

[Daren Todd]

Most set ups only use 6 pins. The center pin is for an auxiliary power or back up lights, and generally isn't used.

Issue could be in the plug. Or more commonly is a bad ground. Before replacing plug, check your trailer wiring. If there is a junction box, inspect that. Also if you have a battery for trailer brakes, check that as well. They could be using a common ground for the battery and wiring.

Also check prongs in the end of the plug. The female portion can get spread out too far and not make a good connection. Can usually pinch them closer together with a pair of needle nose pliers. Also they can get filled with road grime and cause connection issues.

Sometimes the cure can be as simple as spraying both plugs with contact cleaner, and connect/ disconnect a few times to clean the connections.

 

[Daren Todd]

One question. What did you mean by positive terminal?

 

[murph1068]

I should of said power instead of positive.

 

[skeets]

I figure you most likely have checked,, but a bad ground will have you pulling your hair out,, I have chased many of them,look for the simple stuff first

 

[85Hokie]

So all of a sudden I lost my right turn signal and brake light on my trailer. I still had running lights and left signal but parked it and no time to check it out. Today I hook it back up to the truck and I have zero....nothing. I checked the truck pins and I have power to the outlet on the bumper so I suspect the plug on the trailer is the culprit.

I see the center pin is not there nor the pin for the positive terminal. My question is... Does the trailer use all 7 pins? I can't even see in the slot to see if the blades broke off in there. Is this a common problem?

Here is a diagram of all "7" wires.

https://www.ajtnt.com/wp-content/uploads/2015/04/7-Way-RV-Style-Trailer-Plug-Wiring-Diagram-1.png

I too had a problem, it was on the four pole flat.....on of the lugs broke OFF inside the female port.

Like Skeets said - check the ground, the white wire, the ground will drive you crazy!

 

[Lil Foot]

And the trailer end:
(had a neighbor wire both connectors from that first diagram)

 

[Tooljunkie]

Just a quick note, canadian and usa industry standards are different. Right turn and electric brake if i recall correctly.

 

[murph1068]

Ok....my confusion is everything did work perfectly up until yesterday. As I school myself here according to the diagrams I don't have a 12 volt power source on my plug it would seem, nor is there any evidence there ever was one where the diagram says one should be. What I mean by that the blade doesn't look as if it broke off in the plug. The trailer has no brakes, or reverse lights on it so it makes sense those pins are not in the plug.

 

[Daren Todd]

Grounding issue would be my bet. Especially if you had partial lights, then lost completely. Sometimes they wire the trailer to ground through the hitch. That works intermittently. Usually ground on a trailer is the white wire. Especially if they used trailer wire with white, green, yellow, brown.

White is ground, brown is tail lights, yellow is left turn (drivers side) green is right turn (passenger side).

Check/ clean your grounds near the tail lights. And if possible, splice into the ground wire and add a round terminal connector, and attach near the tongue.

Also visibly check the wiring. You may have a pinch where the wires have been cut or rubbed through.

 

[murph1068]

Thanks for your time guys, I will check the grounds first and get back to you.

 

[Tooljunkie]

I usually start with tow vehicle, test all circuits, then to trailer. If you havent split connector, you will likely find wires off inside.common.
My best attempt was soldering small ring terminals on and screwing them then corrosion inhibiting grease.a foot of wire rope tied into the cord and taped securely. Was bullet proof. Nope. Driver never bothered plugging it in and ground it off on the highway. Ya, so glad i dont have to put up with that anymore.

 

[tlefire]

Don't forget if your truck has a tow package, there are separate fuses usually located under the hood.

 

[torch]

Most places that sell tow equipment can supply an LED tester that plugs into the tow vehicle connector. I have round 7 pin and a flat 4 pin versions. They are a fast and easy way to isolate a problem to either the tow vehicle or the trailer. If the lights on the tester work, then the problem is in the trailer or vise-versa. Yes, you can do the same thing with an electrical meter or test light, but -- working in an awkward position hunched down near the ground -- it is very easy to short two terminals and blow more fuses that way. The dedicated tester is just so much easier.

To expand on tlefire's comment: trucks with a tow package incorporating separate fuses for the trailer connection generally have relays in the circuit too. If there's no output at the vehicle's connector for one function, but the fuses are OK, then the original problem may be in a relay.

 

[Tooljunkie]

Also depending on vehicle,trailer lights and rear taillights operate seperately.
If the signals on truck work, doesent mean the trailer plug is working. Bad connector, blown fuses or bad relays. For me,where i used to work it was a near daily thing.

 

[murph1068]

Thanks again guys, I found the trailer to be a wiring nightmare with peanut brittle wiring. I intend to put electric brakes on it in the spring so I rewired from plug to LED tail lights front to back. The seven stud junction box they sell made it simple. All works perfect now.

 

[D2Cat]

murph1068, working on wiring causes me constipation!!

I rewired my stock trailer last year, just as you did, and those junction boxes are nice. Helped to not only make the connections clean to the connector, but helped keep track of what wire went where, and sealed to water and dust!!