I don't have an 88-89 but there must be a constant supply of power in order to maintain the memory when the battery is disconnected. Is it possible that there is a small internal battery some where just for this purpose? After all these years it may have finally quit. Just a thought.
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steve,
91 coup (white with white trim, saddle interior)
91 convertible ( white with white trim, saddle top and interior)
Anybody looking for a southern California car, feel free to contact me. Lots of rust free cars here.