5th wheel wiring hook-up-how do I figure out how to wire my umbilical prperly

#1
I just bought a used Alpenlite 5th wheel and the previous owner "messed" with the wiring on the female umbilical hook-up. How do I figure out which wires do what so I may wire it to my truck?
 

hertig

Senior Member
#2
Re: 5th wheel wiring hook-up-how do I figure out how to wire my umbilical prperly

First of all, how many wires are there? My 5ver had 7, but only 6 were used (ground, batt charge, tail/running lights, left stop, right stop and brake. The seventh wire is often used for backup light.

Disconnect all wires from the batteries in the trailer (so you won't damage your test equipment). Now find out which wire is ground. The easiest way to do this is to use an ohmmeter or continuty tester from each wire to the chassis. Once you have ground, you can apply 12v from ground to each wire until the running/license plate light comes on, the left stop light comes on and the right stop light comes on. This is the minimum harness, 4 wires. Lable each wire as you find it, of course.

To find the battery charge wire, apply a voltage from ground to each unknown wire until that voltage appears across the wires which go to the batteries (they must still be unhooked). This should leave 1 wire, which is usually the brake.
 
#3
Re: 5th wheel wiring hook-up-how do I figure out how to wire my umbilical prperly

One small change to hertig's procedure:

When you are checking for the 'ground' wire, check ALL of the wires in your bundle.

Considering that someone else 'messed' with the wiring, you may have more than one wire connected to 'ground'. You won't want to apply 12v from a 'ground' to another 'ground' without a fused source, anyway.
 
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