Both of the front heat seaters are pretty weak on my LS 400 -94. I have decided to replace them with a non-Lexus replacement part as I was quoted 1000 euro ($1300) for one at local Lexus shop - for the heater element alone, supposedly integrated with the foam and not sold separately. With work cost added, I thought that the approximate 3000-4000 euro for the seat heaters would have been slightly excessive for a car of its age.
Later, I bought two heater elements from a local car parts store, and removed and opened the right front seat. To my surprise, the heaters had three wires, black, gray, and green. It seems that the black is ground, and gray and green are separate circuits as if Lexus had been prepared for heating level control in the heat seaters. The replacement elements have only two wires, and thus only on/off control over the heating power could be achieved with it. Most likely Lexus is already using a on/off control, at least the seat heating button does not seem to offer multi-level control - this is somewhat conflicting with the three wires at the elements.
The resistance of the black-green and black-gray loops are nearly the same, where as the non-Lexus replacement part has roughly half of the resistance of these loops. (This is on the seat back where the loops still work properly, on the base of the seat the loops have been broken)
BTW, two things learned while replacing the heater elements: some corners of the seat frames may be pretty sharp, especially in the upper part of the seat back. If you plan to open the seats, find the sharpest edge first, and cover it with tape before proceeding. ;-) Another finding was that the base of the seat had some surface rust. I would assume that this could have come a problem in more stresful conditions or with more time. I ended up painting the base with rust-proofing paint.
Finally, the questions:
Is it ok to just leave the green wire unconnected, and use the black and gray wires for the replacement heater elements?
Is there a multi-level control of the heating hidden behind the seat heaters on/off-switch?