I have an 86 W150 and am looking to buy a trailer. The previous owner had a seven way flat pin connector with only the ground still hooked up. All the other wires were taped off shortly after the connector. Has anybody wired up a new connector from scratch that can help me out? Is my best bet to look in the service manual and tap into the wires from there? I've searched around and can't find anything on this subject.

 

In my experience all used trailers aren't always wired the same so I use a 12 volt source to figure out how the trailer is wired by applying 12 volts to the trailer pins one at a time to figure out the trailer wiring and then wire the truck connecter to match. If this is a new trailer the dealer can provide a proper wiring diagram. The first thing is to find out which of many different connectors are on your trailer so that you have a match. Then I would pop out both tail light lenses to make access to the wiring easy instead of working on your back. Use a multi-meter to ID each wire as to park/turn signal. The turn signal also provides the brake light signal. Tap into each wire with a pig tail long enough to reach the new connectors location. I like to solder wires and use 2 layers of shrink tubing for water proofing. Then it is simple to wire the connecter in order as per your factory or homemade wiring diagram.

 

It is actually a US M101 military trailer that has been rewired using a 7-way rv connector with backup lights. I can only assume that he hooked it up correctly since I haven't gone to see it yet. Maybe my best bet would be to do the basic 4 wire connection for now and get a set of magnetic lights to get it home. It is a three hour drive one way so I would hate to have a surprise when I get there.

And I will definately be soldering all final connections. The 2 layers of shrink wrap is a good piece of advise I wouldn't have thought of that.

 

Like I said if it is not factory and apparently in this case it is not, you can't be sure but try this sight. If it were me I would build the harness and tap into my truck wiring and ID each wire at the connector end and tape them off. When I get there I would just screw them into the proper position in the plug. This assumes the trailer wiring works but if you aren't sure about it magnetic lights would be the best alternative.

http://www.etrailer.com/faq-wiring.aspx

 

I think the magnetic lights is what I will do to get it home then. That way I know it works before I go to pick it up. That website is a great resource, thanks.