ZCP

Signal lights and brake lights work, but turning on the headlights does not result in the running lights on the trailer lighting up (they activate on the GX without issue). Someplace I should start to investigate if this is a common issue? Would rather not blindly pull things apart to track it down.

mrblister

http://www.etrailer.com/p-TR20117.html

This is a link to a tester you can buy that will allow you to determine that your vechicle trailer harness electronics are working correctly. When you plug it in to your trucks connector there are led lights that will illuminate as you test each function tail, brake, running lights turn signals . If all leds light up and work then your issue is in your trailer wiring. Not in your trucks wiring. Its inexpensive and worth having
14.00 + shipping

ZCP

Thanks. I guess I should have clarified that I did use a tester which did in fact indicate that everything was working except the running lights. So it's on the truck, not the trailer.

swfla

iTrader: (1)

There's an electronic converter box for the pigtail. Most likely your problem. Is the pigtail Lexus original or installed aftermarket? That would help you find it via a Lexus parts site or go to a hitch installer to locate it.

ZCP

Fairly certain it is Lexus original oem hitch and wiring. I will crawl under there to see if I can find anything corroded or broken.

swfla

iTrader: (1)

If you have one. It's likely to be inside. Under a seat or carpeting or behind a panel. Call your Lexus dealer.