Either a bad battery or possibly bad connections. Corroded cables or connections can cause weird stuff. Connections can "heal" themselves and then be bad again.
If it were me, that would be the first thing I would check. A buddy with a starting problem on his diesel came by and we discovered a big voltage drop between battery post and it's cable clamp when he cranked it. He couldn't keep batteries charged enough for dependable starting, and that one battery wasn't getting charged at all. A cleanup of the post and clamp fixed him up.


Kevin
1951 Chevy 3100 work truck
Follow this saga in Project Journal
Photos
1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.