This was a bit of useful information that was sort of difficult to find.
When I first bought the trailer it had a smashed up driver side light module. This module actually caused a horrible short in the trailer electric system which ended up in blowing the fuse for my rear brake lights. I’ve fixed this and the car has no problems anymore, but after fixing the trailer lighting system I noticed I only had one functional light, and it would only turn on when signaling or braking, the rest of the lights didn’t work. I chocked this up to still messed up electrics but ultimately it turned out that the taillight converter in my tow vehicle was shot.
This happens to be a very common thing for the later model Toyota and Lexus vehicles with the 4 pin tow package installed (tail, brake, signal lights only). The old “15 amp taillight converter” with “auto circuit protect” would often fail. I’m pretty sure I fried mine which was the cause of it’s death but apparently others with the similar tow vehicle have had theirs die under normal operation. I also question the auto-circuit protect feature because I managed to burn out the fuse for the brake lights… I wish I could find a module in a junkyard and cut it open to examine the contents to see if it’s somewhat serviceable.
What’s the solution? These taillight converters come in a black factory sealed box, so simply opening them up and fixing them is not an easy task. I have yet to call a Lexus dealer but last I heard they are not in production/sold out/whatever. I do believe they are in stock, just a newer version, but they are probably expensive. Someone was quoted $180 for the module and harness (they are one piece). So in my opinion, the best a person can do is purchase an aftermarket replacement; the ones on eBay come with the factory plugs which will fit into the harness. Assuming they have the circuit protection (which is a MUST in my opinion) this is what I will probably do until I can figure out how to repair the factory module (which I doubt will happen).