I don't have a picture handy, but if you don't have one you can download the FSM for your car here:
http://www.wright-here.net/cars/rx7/manuals.html
Look under section T (Body Electrical) for the info. From memory, the CPU is roughly 6x2x1 inches in size, with 1 or 2 connectors on it; sort of an irregular L-shaped plastic box. Located in the driver's side kick panel.
I had the same problem years ago and fixed it by resoldering all the connector to PC board joints in the CPU, hasn't given me trouble since.