How do you replace the plug on the alternator?

Go out and buy a new plug from an auto parts store. The new plug may or may not come with what's called "butt connectors." If it doesn't come with the "butt connectors," then you may have to buy them separately. Don't forget these "butt connectors." USE THE CORRECT SIZE FOR THE BUTT CONEECTORS. Locate your old plug on the alternator and make sure it looks the same as the new plug. Then, DISCONNECT JUST ONE OF THE BATTERY POLES, EITHER ONE, IT DOESN'T MATTER WHICH ONE. CUT THE OLD PLUG FROM THE WIRE HARNASS AT LEAST HALF AN INCH BACK FROM THE CONNECTOR. Then take the new plug and splice it onto the wire harness using the right size "butt connectors." If you know how to solder the wires together, then please do so because its a good idea to do it. But if you don't know how or don't have a solder gun, it's ok, but when you finish connecting the plug onto the [alternator] wire harness just tape up the splice really good using black electrical tape so that water doesn't get into the splice.

It sounds hard, but its really simple. Just take your time and do it right the first time. The parts or supllies you might need is:

a pair of wire cutters

black electrical tape

a new alternator plug that can be purchased at an auto parts store [auto zone, NAPA, Carquest, Pep Boys, ect....]