[bazar01]

The 1989 and 1990 have two control units.
One opens the spoiler at 50 mph and the other opens the spoiler at 70 mph if the first one fails.
This system was changed for model year 1991.
On the early models, the spoiler control units are located under the right seat.
1991 models and up, the control unit is under the dash.

If you have some electronics skills, you can try opening the control unit and look for the transistors that drive the relays for the up and down operation.
You could be lucky, the failed component is very visible, or could be simple as a cold solder.
Aside from that, you must have an interchange book for the failed component to exactly match the configuration.
A component could be an NPN or PNP with emitter base collectors in the wrong orientation.
So be careful.
Or just bite the bullet and get a new or used control unit for like $300.
You can also send the control unit to systems consulting dot com for repair, (Lorenfb on this board).
Not sure if Pelican has a tie up with him on DME, CCU and other control box repairs, just PM him.