97 electrical problems

My mother-in-law bought a Caravan and had hand controls installed due to a recent pedestrian car collision that left her disabled. There was no keyless remote with it. We took it to the dealership who told us that it came with one and we could buy another one and they could program it. We bought one but they could not get it to work. I was not there but my wife said she was told we needed a new power train control module (computer). Does this sound reasonable? It seems unlikely that everything else on the computer works and the remote section does not. Where can you buy used or rebuilt computers? Where is the Infrared detector?
Thanks