Trailer light problem

[reisertracing]

I just boaught a 1999 wells cargo trailer 28' for my FC hauling. The trailer has the 6 pin trailer/RV adapter that the previous owner used into a 7 pin plug to the hauling vehicle. I have a Chevy 3500 dually and the only lights that work are the barkae lights and turn signals. The marker lights don't work and tha rear tail lights. The inside lights also don't work.

I have gone throught the wiring and it is all connected and grounded. There is a junction box on the front where the wiring harness is attached to the trailer wiring. It is all connected.

What is wrong or what am I not doing right (probably alot). I have bought a new 7 pin adapter and still no success. The adapter has 2 internal wires that can be changed to different positions and I was wondering if this could be helpful.
I have elctric brakes on the trailer that work and an auxuilaary battery that is used in cares the trailer pulls free and will activate the brakes. I charged this up and still no marker lights.

Please hlep with your thoughts and suggestions.
Thanks in advance, John

[Charles Warner]

Johnny,

My 2002 Chevy 3500 dually has an unmarked rocker switch to the left of the steering wheel on the forward panel that turns on the trailer running lights. When the connectors are hooked up the turn signals and brakes/brake lights work fine but the running lights will not work until this switch is thown. I think it has to do with the "smart" lights always on system Chevy uses.

[Steve Demeter]

Don't know about the samrt lights, but figure out which pin on the truck connector is for the tail lights and make sure that it has 12V when you turn them on.

Then make sure that you have continuity between the corresponding pin on the trailer end and trailer ground.

Since the turn signals work, it would seem that you have good ground connection between the truck and trailer.

[Larry C]

Johnny,

Does your truck have a tow/haul mode on the gear lever? If so, make sure it is engaged. I spent about an hour the other day with a customer (I sell trailers) trying to get his lights working before we stumbled across this solution. Of course we could have looked in the ownwer's manual....naw, just kidding, real men don't read or need owner's manuals.

[Charles Warner]

In checking my truck and manual (2002 Chevy 3500 Dually) the Tow/Haul Mode has nothing to do with the trailer lights. It is a shifting adjustment in case of towing heavy loads - more than 75% of the GVW allowance. It recommends NOT using the Tow/Haul Mode when towing lighter trailers.

However, if the trailer light switch is not ON you won't get running lights but will get brake/turn.

[akilcoyne]

When I bought my Ford Superduty, I had much the same problem. It seems that the factory plug on the truck wasn't wired the same as the "industy standard" on the trailer. I changed the wiring on the truck so that is would work on any trailer instead of changing the trailer plug to work on the truck. Maybe the pevious owner of your trailer changed the trailer to work on the truck? You can visit www.etrailer.com/faq/wiring.asp on the bottom of the page it has the industry standard trailer wiring colors along with what is used for colors by truck manufacturer.

[Marshall Mauney]

Have you checked to see what works with the truck running? The interior lights on mine are actually wired to the charging lead from the truck, so it's only hot when the ignition is on. It's frustrating, but so far I've been too lazy to fix it.