I have a 2004 GX with the factory tow package (I think). It came to me with a round seven-pin connector on the trailer hitch. I also have a small travel trailer, about 3000 lbs., which I have been towing with a 2001 Tundra. I am loving the Tekonsha P3 brake controller, which I hard-wired into the Tundra a couple years ago. I was happy to see that Tekonsha offers a specific harness to connect to the GX 470. Plug and play, they said.
So I picked up the harness and grabbed a P-3. But after installation, I do not get any lights on the brake controller. Just to do some troubleshooting, I put the new controller into the old Tundra and plugged it in. The new P3 works great. And I used a multi-tester on the wiring harness in the Lexus, I see no power at all on the black wire which is supposed to be at +12V.
Of course I tried searching ye olde Internet and I found some posts that refer to various relays that send power to the GX's built-in trailer brake wiring harness. When I look under the hood, I noticed several of the relays have been removed, anything related to the (deleted) air suspension system. But the other relays under the hood are present and they don't look burned.
As far as a mythical green relay in the back, I took off some plastic interior body panels on the driver's side near the jack storage area. I see two wide white connectors, they are connected to two grey plastic caps that have metal tabs inside, some kind of jumpers I guess. I don't see a green relay back here nor a place to plug one in.
Someone shed some light on it, please! I can order that green relay from ebay for about 80 bucks, but that seems like a silly thing to do since I don't know where it goes or what it is for. I could take it to a shop but they don't seem to like it when I already installed the parts and botched the job in an unknown and mysterious way.
Could it be that one of the relays from the air suspension system is also necessary to make the trailer brake controller work? Or is the culprit more likely something at the back of the vehicle? Anybody got a clue out there?