Turn indicator peculiarity without brake controller.

[David Schwarz]

I finally took the new truck to test the control harness with the trailer. When I activated the turn indicator, both rear trailer lights flashed in unison (as if the hazard indicator was activated), regardless of which indicator (L or R) was selected. I haven't installed the brake controller yet - is this some sort of "brake controller failure" alert hard wired by Ford? The proper lights were functioning fine with the old truck. I did attach a voltmeter when I got home, and only the appropriate pins were energized by the corresponding selection on the MFS.

I'm half curious, half concerned about this finding. Your thoughts?

[MOUNTAINMAN444]

It sounds like you have a short in the trailer plug. It could be something as simple as one little strand of wire touching across two connectors.
Joe

[mgraveman]

A bad bulb can sometimes do this as well.

[bugman]

Not to mention a bad ground. Bad grounds are the number one problem with trailer lights.

Jim

[David Schwarz]

It turns out that I didn't have the harness completely pushed into the receptacle. When I bought the used truck, the receptacle was mounted on some thin (~16g) steel that flexed when you pushed in the plug. I moved the receptacle to the bumper where it is easy to apply the necessary force to mate the two. Once done, everything was working fine. Thanks for all the input though - I didn't want to leave this topic open ended.