If they aren't turning on at all try starting from the fan and work your way back to find the break down. You know the fans are working. I'm also assuming fuse and relays are working. What about temp sensor? Or have you already narrowed the problem down to the resistors? I'm not too familiar with the 140 set up, but I can't imagine it would be that much different from any other set up. If fans aren't turning on at all there is a breakdown at some point where the signal is being sent to the fan to turn on. Possibly a grounding wire.
*Edit*
See if this link helps:
http://www.peachparts.com/shopforum/tech-help/152361-c-low-fan-not-working-w140-m104-1995-s320.html