Voltage fluctuations with engine not running

[69chevytruck]

I ran the truck for about an hour moving downed limbs, so a lot of idling. the truck died as I had burned up the fusible link at the battery.
Replaced the voltage regulator and the truck started. it ran long enough to move it out the yard. Sat for a few weeks. Started it this afternoon, it ran for a minute and burned up the fusible link to the battery.
I did the alternator conversion for an internal regulated alternator. the truck started and ran for a minute, then died. Now all accessories work, the truck cranks, but does not start. I get fluctuations in the gauges (volt and Tach) when in ACC, and a clicking noise, then it all dies. It doesn't stay live long enough to tell where the sound is coming from and I really don't want to leave the ignition on too long.
I will be checking grounds and connections.
Any reason to suspect the starter? Sometimes it clicks, doesn't engage, when I try to start the engine. Once it engages, it cranks.

Any other ideas?