Voltage jumping around...goes up to 17.50!!

[bryanw1968]

The truck runs fine but a few weeks ago I noticed that the voltage has started to go all over the map. From 12, to 17.50 and everywhere in between. I replaced the starter thinking that the internal voltage regulator was shot. Had no effect. I've checked all my wiring and everything "appears" to be good. I have electric fans and disconnected those thinking that maybe one of the relays was causing problems but still nothing. Now, the strange part. When I turn the truck off and then turn the key to on, the starter seems to make a chunk kind of noise. Could the ignition switch itself be the problem or possibly my starter. As far as I know the ignition switch is 40 years old. The starter is a CSR high torque mini starter and is only a couple of years old. Any advice is appreciated! Oh yah ignition is all MSD, not that I think ignition could be the problem.
B