Trailer hitch wiring, the grey wire?

[Ray in Phoenix]

What is the grey wire for in the trailer wiring?
It runs up to the front of the car, but where does it connect?
Maybe I am just missing something, but the instuctions don't tell you much.
Thanks :help:
Ray

[djc208]

I think there was a similar question a few weeks ago. In any event the wire is for an electronic brake controller that would be wired in under the dash to a brake control unit for trailers that have electric brakes. For smaller trailers this isn't needed.