I had the same prblm u describe on my 88 745t

(the bulb shouldn't have anything to do with it)

I removed the seat heater relay and probed the

connector with an ohmeter and verified power

pins and continuity thru the seat heater.

everything checks out but the relay continued

to cut out < 5 secs even at coldest ambient and

packing the relay in ice!

I ended up removing the relay and installing

a jumper on the connector so heater is always

on. I regulate the temp by cycling the

console switch manually and seat heater works

fine nice and toasty. I'm convinced the seat

heater relay is faulty and frankly dont

understand how Volvo intended this relay

to regulate the heat properly since it does

not contact my leather seats to sense its temp

I intend to replace it with the high temp

button thermostats I used on my 240 as soon as

I figure out where to mount the thermo in the

seat pad the older 700 cloth seats have button thermos

and not this relay

Mike