Phantom activity when Trailer lights are hooked up

Joined
Oct 28, 2016
Messages
97
Location
Oregon
I have an 2003 LX470, which has the factory 7-pin trailer light adapter. I extended these lines when I installed the frame mounted hitch. I also installed a P3 brake controller into the factory harness.

When I hook up my trailer, everything works perfectly, (lights, brakes, etc). However, when I turn the car off (key out of the ignition) I notice that my rear windshield wiper is running on intermittent, my heater fan motor is running on low, and I can't lock/unlock the car with my FOB. Once I disconnect the trailer lights, all is well, and sometimes if I open the rear hatch it all stops. The problem is repeatable.

I don't even how to start troubleshooting this issue. Anyone else ever had this problem?
 
Joined
Apr 24, 2016
Messages
125
Location
Portland, OR
My guess is that something in the wiring of the trailer brake system itself is "lifting the ground" for your devices.

I'm here in Portland, and if you'd like to look through the factory service manual (and more so the factory wiring diagram) and try out a different 7-wire trailer (to eliminate the trailer vs. the controller), I'm around.
 

e9999

You want to do what...?
Moderator
 
 
Joined
Sep 21, 2003
Messages
16,744
Location
US
Discussed a similar issue some years back and how I solved it. I think there was even a TSB put out on it.
 
Joined
Dec 2, 2003
Messages
3,429
Location
Rockville, MD
The battery in your trailer is backfeeding the system and powering other things that are in the same fuse block.

If you unplug your trailer prior to shutting the truck off, you will find that all the gremlins go away. There is a factory plug 'n play relay fix for this that goes inline with one of the body harnesses in the rear driver's side quarter panel IIRC.
 
Joined
Oct 28, 2016
Messages
97
Location
Oregon
Awesome, thanks guys. So it looks like I need a relay. I'm assuming the dealer would be able to look up that number "PN-82241-6010"? A quick google search didn't bring anything up.

Edit: never mind, found the part, forgot a 0 (60100)
 
Last edited:
Joined
Oct 28, 2016
Messages
97
Location
Oregon
Well, I just installed the factory relay and the problems still seem to persist when the trailer is hooked up (VSC light on, marker lights on, rear windshield wiper running, blower motor running). Not really sure where to go from here, though I had it solved.
 
Top Bottom