97 Gt Electrical Problem

Check your fuses and relays is all I can think. Unless there was some major sparkage and grounding when swapping the batteries...this would cause some bigger issues.

Good Luck!

I give up. What Model year Mustang are we dealing with? The electrical layout is very different in a 96-98 than a 99-04.

Since I don't know the MY of your car, I can't tell you WHICH fuses to check. So check all fuses in the engine bay and driver's kick panel.

Double check the battery terminals especially the battery negative as it's bad about splitting when over tightened. Double check the grounds around the radiator core support.