E36 Autobox problem

[sparkythecat]

The autobox warning light has come on my E36 328i touring and it's gone into rescue mode. This happened once before about 12 months ago and the independent who looked at it fitted a new autobox ecu at a cost of around £600. This time I'm convinced it's a wiring fault as the light goes out and comes back on again when you go over a bump in the road.
Bit of a numpty question I know, but where is the gearbox ecu located on the car and whereabouts should I be looking for any loose connections?.