NEED HELP PLEASE. 17 volts on alt. overcharging

[steveo3318]

Ok I just got my 67 in and blew a cheap battery out of it. Figured it was just cheapo previous owner installed. Well I put a dura last agm gel battery in and fired her up. Since my volt gauge stayed dead center all times I figured I would put my volt meter on the batter. And wow it would put out up to 17.8 volts as I increased rpms. I know this is not correct. Can anyone give me some guidance on what to check and what color wires to check. Maybe a fuse is blown on the gauge. How do I check this out.