Thanks to everyone for recommending that I get my alternator fixed. It only took a few minutes to remove and I brought it to a local alternator shop and they only charged $30 to replace a diode. Now it works fine and I don't have to worry about it anymore.
PS It wasn't a Delco one wire alternator. It was a Lucas 3 wire and many years ago someone had removed 2 of the wires. It still works fine with just the one wire. When you start it at an idle it doesn't charge but the second you increase the engine speed it starts to charge and remains charging correctly at all speeds. The shop told me how to connect it up right so that it will charge from the second it starts but that is a lot of trouble to go through for no reason because it has worked fine like this for the 16 years that I have owned it.