Another trailer wiring question

[Bob Pederson]

Yes, I did do a search for this info but no luck. I have a '94 Exp with tow package and the common 7 pin plug under the right side bumper. I have and have been using the mating factory connector with harness for a 4-wire trailer connection. No problems there. I just got a new trailer with trailer brakes and aux battery so I need to wire my old factory harness up to a 7 pin trailer socket.

My question is: What are the three black wires which are shorted to the white ground wire doing in the factory tow harness? Are they there to make the light isolation relays work? My Chiltons manual doesn't show the wiring of the trailer connection haraness. So,.... do I have to run separate wires for brakes and B+ around the factory connector to my brake controller and battery? Any and all help would be appreciated. I've already spent way to many hours of my vacation trying to get this to work.

[Bill Kemp]

Here is some info on the trlr wires. http://draco.acs.uci.edu/explorer/trailerwiring.html
Seems to me that your going to have to run new wires for the brakes & battery. You may want a battery isolator also. Google "battery isolator".

[Crankcase]

First of all....you will need an Electric brake controller for those brakes....That will require running a few wires in the cab and a seperate one to the trailer harness.

Second, just keep the factory harness, and cut off the 4 pin end close to the connector....put those wires into the new 7 pin socket in their appropriate places.

Third, wire up a solenoid to power the trailers battery, and run a good sized guage (10) wire to the 7 pin harness.

If you need soleniod help, I can make up a diagram.

[Bob Pederson]

Bill and Crankcase.

That was exactly the info I needed. I was having a hard time understanding why the original Ford harness had three ground wires wired together. Late last night I finally considered the possibility that it had to be something related to the isolation circuit and it is simply a coincidence that the Ford harness has 7 wires just like the trailer connector.

Crankcase, I would appreciate a schematic or verbal explanation of your proposed solenoid installation. Should I just use a starter solenoid or did you have something else in mind?

Thanks for the quick response. I should have done this three days ago.

[Crankcase]

Well...Since the trailer has batteries on board, you would run the circuit like the pic below:

The switched 12V+ would be connected to a circuit like the wiper feed that only comes on in the RUN mode of your ignition. That way you are only connected to/charging the batteries when it is running.

I will make up another crude drawing in a few mins...

[Crankcase]

Forgot the pic

[Crankcase]

Any questions...just ask.

[Crankcase]

Cleaner version:

[Bob Pederson]

Crankcase. Thanks for all the info. It helps a lot.
Bob

[Crankcase]

No prob.