Could be a bad engine rpm sensor. It attaches to the bell housing below the oil filter housing. Check continuity across the refrigerant low pressure switch behind the left headlight, the one with contacts on the sensor rather than connectors on a pigtail. With the AC switch on, one of the wires to the low pressure switch should supply +12V. If not, the problem is in the cabin.

EDS and ABS won't function if the OVP goes out. Maybe SRS won't function either.

Jimmy, the OVP relay is in a cubby aft of the battery. There's a plastic shield sealing the cubby from the engine bay.

Sixto
87 300D