Welcome to the site. Nice find on the 92MM! With only 54K that's quite the score.

Going by wiring diagrams for a '91 (and assuming they're the same for your '92), power to fuse #9 (heater) and #20 (rear anti-lock brake system) is from the ignition switch via a blue wire with a red stripe. Test for power to fuse #20. If no power to 9 and 20, test the ignition switch for power to the blue/red wire with the key in the "ON" position. If no power, check the switch. If power, disconnect the ignition switch connector and check continuity of the blue/red wire between the connector and fuses #9 and 20. If there's no continuity to either or both, check the fuse box connections of the blue/red wire, then look for a fault in the wire.

Good luck