Trailer hitch wiring troubleshooting help needed

[k9sar]

Greetings. I recently picked up a 2017 pathy at auction and am working to fix all the stuff I can Today's issue is trailer hitch wiring. It has an installed u-haul hitch and wiring harness that plugs into the ports behind the trim on the drivers side rear and to the 2 plugs under the passenger side bumper (there's an instructional video from u-haul and I followed along, checking all the connections and relay installations.
Symptoms:
there are 4 important ports on the 7-pin connector... ground, lights, LT/brake and RT/brake. I placed a test light on GND to Lights and when I turn on the running lights, the test light illuminates. I place the test light on either of the turn signal pins and I get no illumination with turn signals or brake. I unplugged the u-haul harness from the car harness (passenger rear under bumper) and tested on those pins as well. Test light to ground and I probed every pin in the connector (5 of them) with no success.
I swapped around the 4 blue relays (2 in rear panel and 2 under hood) and behavior did not change. I ran a multimeter on DCV from the NEG battery and probed every socket on both relay slots for LT and RT trailer under the hood. There was no noticeable voltage.
Has anyone had to troubleshoot the trailer lighting system? Any suggestions on if I should even be seeing voltage on any of those relays? I'm in need of a working system to move my son this weekend and all I can get is running lights

[Slartibartfast]

I don't know crap about the R52, but I did spend entirely too long troubleshooting a trailer wiring fault on my mom's Lexus that resolved itself when I turned the ignition on. I guess it's got a powered trailer light controller? Something to check if you've been testing with the key off.

[k9sar]

4 hours ago, Slartibartfast said:

I don't know crap about the R52, but I did spend entirely too long troubleshooting a trailer wiring fault on my mom's Lexus that resolved itself when I turned the ignition on. I guess it's got a powered trailer light controller? Something to check if you've been testing with the key off.

key on and accessories on so I can get turn signals and lights but thanks for responding. sometimes it's the easy stupid stuff. unfortunately, not this time so far

[Slartibartfast]

Yeah, that makes sense. Have you tried with the engine running?

 

Nico's manuals stop at '16 unfortunately, but there is a description of the trailer lighting system on EXL-12 of the '16 manual, and wiring diagrams start on EXL-94. Might get you started.

[k9sar]

Solved.  There is a fuse box under the hood that is on the passenger side top and contains a 10A fuse that feeds the other fusebox with all the relays and other trailer stuff.  I checked that fuse and it was fine BUT, after plugging it back in, the behavior changed. Turns out the fuse socket for that 10A was corroded and not making good fuse contact.  Cleaned it up, bent the tabs and reinserted the fuse. Now everything works as expected.