I have a 7 pin traiiler connector on my 1999 Super Duty. I want to add a wire for backup lights on the trailer. From what I have seen the center terminal on the 7 pin connector can be used for this. I have seven wires in the connector (truck side) that plugs into the truck wire harness. yellow, green, orange, blue, brown w white stripe, white and black with green stripe. I tried testing with a continuity tester and none of these wires seem to be for the center terrminal on the 7 pin connector...Any thoughts?

 

So if you have reverse lights lit on your truck with someone making sure no one gets run over or such, the center pin on your truck receptacle does not go hot?


Steve

 

No, Is it suposed to?

 

I tested the center pin with key on reverse lights on and got nothing. I found this diagram and it seems to match mine. I will have to get out there and check again especially the black w green wire..

 

Still not getting any power to the center with backup lights on, no continuity with the black w/green wire?

 

That pin is relay-isolated from the back-up circuit. There HAS to be a relay plugged in for that to work.

In fact, ALL the trailer circuits (except the brake controller signal, and ground) are relay-isolated from the equivalent circuits on the truck, just for safety, so a trailer short doesn't disable the truck lighting..

It uses the same fuse that the trailer running lamps do, so if they are working, you are likely just missing that relay. It should be in one of the under-hood "doghouses" next to the under-hood fuse box.

Need the wiring diagrams? See below.

Pop

 

When I pull the plug from trucks wiring harness and test each contact with a continuity tester with the middle contact on the connector I get nothing?

 

I am having a hard time getting my head around this. First of all, do you have any lead that is powered when you are in reverse, that would be a voltage check. If the answer is no, you would have to check relays and fuses under the hood. That would be the first step as regardless of continuity, no voltage would mean no lights in reverse. I am not clear how you are using your meter.


Am I on the same page?


Steve

 

He prob has a combo volt/ohm meter.

 

I unplug the plug that connects the 7 pin connector to the trucks wire harness. Inside the plug there are 7 contacts. I check each one with a continuity tester to tell me which one goes to the center post of the 7 pin connector. I should get a audible beep when I touch the right one. I don't. So no point of going to the realays or fuses yet if there is no connection between the plug and the trucks wire harness...

 

So you have seven contacts and seven pins, but no continuity to the center pin from the back of the plug. When you check contact by contact, you should have six that have continuity to pins and and one that does not. Is that the case, when checking with your meter?


Steve

 

That would probably be true if I checked the other pins but I am only interested in the center pin for reverse or backup lights. I know all the other ones are working because all the lights on the trailer are working...

 

So, you haven't answered: Is the relay in the doghouse?

Pop

 

I can't tell how important this is, but my thought was, if you have a bad seven pin on the truck, it could be replaced. Then check for a powered lead or tap the back-up lights on the truck. Maybe more messing around then you want to do however.
Steve

 

I'd be hesitant about tapping into the truck's back-up lighting. The relay isolation is there for the safety of a multi-position switch that's on the trans.

An over-current condition from a faulty wire on the trailer could cause a new DTR sensor switch to be purchased.

Pop