'88 Mondial- Multiple warning lights

Sounds like a power supply problem, see if you can disconnect the reverse light switch and see if the other lights stay off when you put it in reverse. Sounds like a fault on the reverse switch.

 

Or some binding/straining of a wire bundle. Either in the clutch pedal pivot area or down in the center console where the shifter is. Sorry, I don't have my wiring diagrams with me at the moment...

 

There is a secondary electrical board underneath a metal panel under the carpet in the upper part of the passenger footwell. Might take a look in there, unplug and replug in the various relays and connectors. I know for example the brake warning and seatbelt relays are in there. The slowdown light control is in another secondary board in the left side of the trunk, you have to remove some small screws and peel back the carpeting to take a look. Would first undo various connectors, clean with electrical cleaner and dab on a bit of Deoxit, and put pack together before doing anything further. Something may have just been jostled or vibrated loose.

The reverse switch does look suspect, as one would think it would still actuatre the reverse lights.

There is a "key activated services" relay in the main fuse box, might be the one that links some of these lights together? Might also remove the relay or swap it with one of the same type and see what happens.

 

I have a wiring diagram book so can send you a copy if u drop me an e mail address