Put battery in wrong way 05 Mazda3
 

In a rush to going I have put the battery in the wrong way:mad: Called the RACQ and they showed me the 80amp fuse needed to be replaced. I have replaced it as well as the fuseable link on the battery cable. The radiator fan stays on and there is no movement or sound coming from the starter. How bad can it be and what else should I replace. If the ECU is cactus can I replace it with a used one from a wrecker?
Thanks for any help. Looks like a trip to the auto electrician.