So it sounds like the problem is probably in the seat itself.
First, is this a reasonable conclusion?
Yes, given the harsh environment the seat heater lives in.
Second, what could be wrong (bad heating element in the seat?),
and what's the process of repairing?
Remove seat, remove cover(s), replace heating pad(s), reassemble.
It's very much worth unplugging the heating elements (there
are two: back and butt) under the seat and measuring their
resistance first. The two-stage heater puts them in series
on low, and in parallel on high. Does the system not work
on both settings? I'm not sure how intelligent the relay
is about reacting to electrical problems in the heating
elements, but it could be that one fault will take both
elements out of service.
If they both measure good you may have a bad relay. Those
are clipped to the floorboards under the seats in a 126, I'm
not sure about anything else.
-- Jim
