I'm posting this on a few different Lexus forums to reach the largest possible audience and get the most information I can. I just bought my GS400 a few days ago and it's in fantastic shape except for a few general maintenance/wear items and this glitch with the A/C blower. I know I'm not the only one to have this issue but I haven't seen a definitive cause and solution. So I want to solve this issue once and for all for the next person that it will inevitably hit.
So here's the case to solve. With the 10A "heater" fuse still installed in the driver's side fuse box, the blue/black wire that is supposed to feed 12v positive to the blower controller/resistor is grounded whenever the heater relay switches on. I have tested for continuity and it does indeed go to ground.
However, when the 10A "heater" fuse is removed, the blue/black positive wire receives its proper 12v when the heater relay switches on and the blower activates and works perfectly.
I need to know: What is in that "heater" fuse circuit that would cause the 12v positive blower wire to switch between ground and positive? That main hot wire, according to my extensive research, supposedly goes from the resistor/controller to the heater relay and then directly to the 50A HTR fuse and from there to the battery. Is there something in there that I'm not aware of? What could be affecting the relay's function?
I've got bits and pieces of the factory service manual and wiring diagrams but nothing complete. If anybody can point me in the direction of the official Lexus-issued manual while we're at this that would be great.
Thanks in advance. Let's track this down and solve it once and for all.