To bring this thread where it belongs and not hijack the RX400 thread previously here goes...

Back story - this year bought my 2004 RX330 however the drivers seat leather was completely shrredded and heater element not working. I replaced the seat leather bottom ($50 looks perfect but quite a chore to do) and installed heating elements ($50 for all 4 elements on Amazon). Passenger seat heating elements work fine, no power to drivers seat heating element. There's no power going to the seat heaters (no power to green plug shown below) nor any power going to the gray plug under that green plug going into junction box either, I've swapped out both those junction boxes so I know that box is not the culprit in this case. Anyone with a schematic for a 2004 RX330 seat heater? I do believe the switches in the dash are functioning proeprly as per my ohms reader so the problem is between the gray plug and the dial switches someplace. Thank you for that response below in the other thread hoping to assist...



That junction box under the seat with the green and grey 4-wire plugs is actually a Controller (if part number on it is 85864-05010). Common in many Toyota/Lexus cars with the little dial seat heat control (vs mechanical switch). Just had one go out on my drivers seat due to overheating (smelled something hot and seat heater would not turn off.). A somewhat expensive part, but simple inside with a 7-pin semiconductor (VN570) that regulates the voltage to the seat heating element based on the signal coming from the small dash control ****. Cursed with thinking I can fix anything, purchased two of these semiconductors from a China supplier and replaced the one in the drivers seat control module. (had to break away some of the plastic to get to it, the bottom plastic pops off). I reused the metal heat sink using thermal paste AND a small nut/bolt thru hole I drilled to keep it tight. Plugged everything back together and works perfectly. Link to the semiconductor is (get the TO220-7version) https://www.transistormosfet.com/en-...uct_id=3917212

Separately, I also installed the simple aftermarket elements with the hi-off-low switch in an RX300 that had no seat heaters. They are still going strong after 10 years. Can confirm it is an arduous, but doable DIY job. I used heavy duty zip-ties to pull the seat leather back onto the wire frame instead of metal clips. Those are still going strong also.

pictures of the Seat Heat Controller and semiconductor.

 

Excellent work @Leeper .

If you still need wiring for that piece let me know but it looks like you posted a fix.

 

Heatsink should be 10x bigger. I'm amazed that driver lasts as long as it does, tough component.

 

I need the wiring schematic that shows from the switch to the element not for that one junction box, the box is functioning it's just not getting power to the gray connector that goes into it on driver's side