would not start because key was left on?

Hello,

When a cable gets hooked up backwards during a jump start, it can potentially cause a number of damages.
First of all, it is likely that some fuses or circuit breaker got tripped or blown.
The best course of action would be to use a test light and check all the fuses.

Here is a helpful guide:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Also, you want to make sure to check for any burn wires or connectors.

I have attached the wiring schematics for the starting system below.

Please let me know if you have any questions.
Thank you.