The switch on top is the overdrive lockout switch. 1 wire goes to the solenoid on the overdrive, the other wire goes to the overdrive switch on the steering column.

The other switch on the side of the shift cover is the reverse light and seat belt reminder light. 1 wire has fused power coming from the fuse box, 1 wire goes to the reverse lights and the other wire goes to the seat belt warning light on the dash.

The reverse/seat belt switch has 3 male blade terminals and originally there was a paper label with colored dots representing the corresponding wire color next to each terminal , but that is probably long gone.

I've got those switches in stock and I'll see if the switches also have numbers cast into the switch that identify the terminals.

You can just try swapping the wires around until both reverse and seat belt lights work correctly.
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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com