I have a 1991 C2 automatic with 19,000 miles. Recently, I have a number of problems with the electrical system. All of this happens at once. The car runs fine, but with the following multiple issues.

The tiptronic transmission doesn't work, though the car still runs as if in automatic if put through the tiptronic cycles. The speedometer, odometer,and cruise control do not work, however the tachometer does work. The turn signal that operates the on board computer functions does notdisplay the distance to next fill-up, average fuel consumption, tripometer, digital speedometer, or average speed. However, the outside temperature function still works. The rear spoiler does not come up as designed and must be manually engaged. There are two lights on the dash, in addition to the central warning light light (!). The other lights that appear are the rear spoiler warning light and anti-lock brake warning light. The brakes have been changed and the lights were all on before and after the brake change. All of these things appeared at once and seem to all be related to a singular electrical issue. Any ideas on what this could be?