I can get by without heated, leather seats on my '93 940 but it would be nice if they worked. I got my wiring diagrams here:
Volvo Wiring Diagrams
and everything, including color, almost matches, except for the Black/White positive lead coming out of the on/off switch and connecting to the seat. Both driver and passenger's seats have that wire reversed with the Blk negative lead, so I don't think it was a mistake. The rest of the wiring and terminals match so my question is "Will the heaters still work with pos and neg reversed? If so, then my problem has to be the relay because I do have continuity thru the whole circuit when I bypass the relay. I did put the relay in the freezer for a few minutes to activate the thermostat but I still couldn't get continuity between terminal 4 and either 3 or 1. Does the relay still need to be powered to connect that circuit even if it's cold enough? Thanks

 

Since the heating element in the seats is just a resistive wire, polarity really doesn't matter. It should work either way.

 

Well that's good to know. Thanks. And I'm guessing that if the circuit is complete it should work. Oddly, when I had the seat out and the relay unplugged I hooked up a 12 volt jumper(neg and pos) from my battery directly to the seat connectors and after 3 or 4 mins still didn't get any heat?

 

I haven't worked on a 940 but I know on the 240s there is a thermostat on there to keep your buns from being cooked. Take a look at the link below on how to repair seat heaters. Again, it's written for a 240 but I think most of it applies to 940 as well.

http://cleanflametrap.com/seatHeater.htm

 

Actually, in a 940 the thermostat is inside the relay. Good info though. Thanks