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Author Topic:   Trailer Lighting
Jim McClellan posted 07-29-2007 12:16 PM ET (US)   Profile for Jim McClellan   Send Email to Jim McClellan  
I just rewired my trailer lights and have the following problem:

When I turn on either blinker, the lights on both sides of the trailer flash (giving the appearance of hazard lights).

My connections (on the trailer) appear to be correct, although I haven't connected the amber side lights in the middle of the trailer.

This brings me to the second problem: The instructions are not at all clear about which wire I should connect the amber side lights to. There is a single black wire coming out of the light. I'm assuming the lights ground on the trailer and the black wire should go to the power wire. But I would like to know for sure before I cut into it.

Any help here would be greatly appreciated.

jimh posted 07-29-2007 03:05 PM ET (US)     Profile for jimh  Send Email to jimh     
It is fairly common that the lamps on a trailer use the trailer chassis for the negative connection and only a positive lead is provided to connect to the trailer wiring harness.

There are many kinds of connectors used in trailer wiring. What connector are you using to attach the trailer wiring to the vehicle wiring?

Jim McClellan posted 07-29-2007 10:43 PM ET (US)     Profile for Jim McClellan  Send Email to Jim McClellan     
I have a 7 to 4 (round plug) connector. I don't know if it's right or not, but it's built in to the 1998 Ford truck I have. I can't see any way to (easily) bypass the plug and connect the flat four on the trailer to its counterpart on the truck.

Does that make sense? On my 2003 GMC, I had the option to go around the plugs and connect flat plug to flat plug.

Thanks for the info on the sidelights.

jimh posted 07-29-2007 11:01 PM ET (US)     Profile for jimh  Send Email to jimh     
With a flat four connector on the trailer, you should be wired like this:

WHITE = common; connects to trailer chassis
BROWN = tail lamps, side lamps
GREEN = right turn signal, brake lamp
YELLOW = left turn signal, brake lamp

If you have the turn signals/brake lamps wired correctly and they both operate, check for a poor ground.

Jim McClellan posted 07-29-2007 11:42 PM ET (US)     Profile for Jim McClellan  Send Email to Jim McClellan     
The ground wire is connected with a bolt into the tongue of the trailer. Bare copper wire to steel. I'll take it off, wire brush the bolt and put it back on.

Is that the ground you were talking about? Or do I need to check something at each of the lights?

Sorry to sound like an idiot, but electrical wiring has always eluded me.

towboater posted 07-30-2007 01:51 PM ET (US)     Profile for towboater  Send Email to towboater     
If your trailer lights are flashing, your ground is ok...you have connected your stop light/turn signal to the tail light loop.

It would be nice if every trailer and OEM light setup followed Jims schematic...but often things get changed around and you have to deal with it.

Disconnect and trial/error the other wires without regards to the wire colors til your trailer lights are working properly.

Jim McClellan posted 07-30-2007 04:34 PM ET (US)     Profile for Jim McClellan  Send Email to Jim McClellan     
Okay, thanks!

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