The cause of your problem was possibly suggested twice above, and is likely the pre-resistor for the low-speed fan (white ceramic rectangular-shaped part with a heavy coil in the middle attached at each end to an 8mm nut, often covered with a metal cover in the middle to protect the relay from fire damage in case any debris falls into it). It is located on the 126 chassis in the most awkward place on that vehicle, underneath the brake booster, and is one of only 3-4 jobs on that vehicle that is truly cuss-worthy. You could also have a short in the wiring between fan and fuse box, and that would still be easier IMO than replacing the preresistor (which gets corroded and does not come out like it does when new).

__________________
Don't ask me, I'm a shop-owner by default