Yesterday I noticed my GEN dash light on after I had been sitting still w/ engine at idle and AC on for about 5 mins. It went off as soon as I hit the gas and got going again, but I noticed my dash volt meter was reading about 13.5V. I've also noticed a slightly longer crank time for the engine to start over the last couple of months, so I'm guessing that both conditions are either the result of my alternator slowly going bad or a bad connection at one of my power cables, as they're all original. I'll be checking my alternator health at a local parts store later today, but first I'd like to make sure it's not a bad power cable connection.

What power cables do I need to scrub the terminals clean to make sure it's not a connection issue? I know there are 7 power and ground cables in total in the engine compartment, but I think the main culprits here would be just 3 of them?

Thanks