Saab: Saab NG900 electrical problem, seat heaters, electrical problem

Question
Hi, please can you help me track down an electrical problem?  I have an early 1994 Saab NG900s 2.0L (90k miles) with heated front seats.  When the engine is running and I switch on either of the heated seats all power to the wipers, indicators, heater fan, hrw etc. is lost - but not the lights.  When the seats are turned off power returns in a couple of seconds.  (New battery fitted in the last few months.)

Answer
Clive:  I am sorry, but I only have close knowledge and info on SAABS up to 1993. However, the data for 1993 (which I believe is applicable to 1994 models) notes that the one item common to all those items affected AND the seat heaters is the ignition switch itself, terminal 54. I believe what is happening is that the ignition switch is faulty in that the load of the seat heaters (ordinarily not a problem) is causing the contact to fail, either because of high resistance or local heating. You can check this by uncovering the switch (removing the inter-seat console cover, AND with the car running, placing a jumper between terminals 30 and 54 and THEN turning on the seat heaters. If the other items stay on as they should, then you have confirmed the location of the problem in the ignition switch as hypothesized.
 If that doesn't happen, I am stumped and would need to do local tests for shorted wires somewhere on your vehicle.

 Hope this helps.