Reversed polarity on your car now your car wont start with new battery?

Answer 1

There are quite a number of diodes and transistors in the critical circuits of your vehicle. Any one of them can be destroyed by applying high current reverse polarity.

You'll need to go through every individual circuit and check for damage. Start with fusable links and other fuses, then find out what it takes to engage the starter.

Once you've got that far, start checking the ignition circuits, make sure you have good spark to the plugs, and finally, check the injection system. Most automotive computers have built in protection against reverse polarity, however...

Good luck.

It's a simple mistake but it can be quite expensive.