No worries ... I don't see you being difficult at all. We are all trying to learn and help each other that is why we are on this forum. If I am wrong , I myself would say "I am wrong, my bad " just like you did on your first sentence on your previous post which is a very good attitude coming into a forum. Only d?ckheads do not know how to admit being wrong.
I would suggest you scan or take a picture of those 4 pages from your 98 SC Electrical Wiring Diagram manual and post them here so we can check them out and can compare them from the info coming from the Toyota Website and all learn.
Here are the pertinent pages from the 1998 Lexus SC300 / SC400 Wiring Diagrams
coming from the TIS
Toyota / Lexus Technical Information System which belongs to Toyota. It's their OFFICIAL Technical Info System. On that site you will find whatever info you want to know about any Toyota / Scion / Lexus car for whatever model and year from 1990 ... basically anything from descriptions , technical info, wiring diagrams, diagnostics and solutions to problems and others.
Webiste Link :
Here is the particular page for the Driver and Passenger Seat ECUs of a 1998 Lexus SC300 / SC400.
If you trace most of the wiring from the Driver Seat ECU as shown above , they go to the power tilt / telescopic ECU and battery voltage supply as shown on the next picture .
The only pin I see from the Driver Seat ECU that goes to the Engine ECU which houses the transmission controls is on orange outline below
That wire that I outlined goes to the STP light switch and the STP Pin of the Engine ECU as shown here
Here is where it goes to the Engine ECU ... which is the STP Pin as show here
And that STP Pin has nothing to do with the operation of the Seat ECUs . It is common for cars with either Manual or Auto Transmissions. It provides an INPUT
data to the Engine ECU and not vice versa.
Here is what that STP Pin is for :
Pin 4 - STP , Stop Light Switch , Input , This pin is used to detect when the brake pedal is depressed. Used to disable the automatic transmission lock up torque converter and exit deceleration fuel cut mode etc. This pin is connected to battery voltage when brake pedal is depressed, the ECU pin is open circuit when the brake pedal is not depressed.
My personal observations so far :
a) Manual Transmissions SCs were manufactured only up to 1997 . So if one is able to use seats from 1998-2000 which all have auto transmissions, that clearly says .. Engine ECUs that houses the transmission controls has nothing to do with Seat ECUs
b) I have a 1997 SC with manual transmission . I have moved around the seats from a 1992 , 1994, 1995 with auto transmissions to that 1997 SC and all worked . The 1992-1994 though have fewer controls compared to the 95-2000.
c) As per my experience , Toyota Part numbers may differ in different years .. but that doesn't necessarily mean they differ in construction or materials or functionality. A good example will be to compare the components of a 2jzgte Non VVTI ( 1993-1997) and 2jzgte VVTi (1998-2002) engines. Some of their internal part numbers on their catalogs are totally different but are exactly the same parts meaning there is no difference except the part number.
d) The differences I see on the wiring diagrams are only on the Passenger Seat of 1992-1994. They have less switches and motors . Though the Passenger seat ECU still looks the same based on its ECU pinning. The 92-94 only have slide and recline controls based on the diagrams on that site. The 1995-2000 has slide, recline , front vertical, rear vertical and lumbar support . But Driver side ECUs and controls are same. If I miss something , I stand to be corrected. But so far , on account of my investigations , if the OP has a 1997 car , he can move any 1998-2000 SC300 / SC400 seat and all functionalities should work. And for easy comparison below I posted the seats wiring diagrams from a 1997 SC and 1998 SC which led me to conclude they are the same....
1997 SC Seats wiring diagram
1998 SC Seats wiring diagram
For the sake of learning , I would strongly suggest take a picture of those 4 pages you are referring so we can compare them with the info from the Toyota / Lexus website so we can all learn .
Also here is the wiring diagram for the same year model 1998 that has heated seats. The heater components has their own switch on that transmission shifter cover. I don't see any connections to the seat ECUs .