1966 c10 chevy truck
Engine or electricals?
Either way I would check the battery electrical connections, battery and alternator voltage and the ground strap.
A/c Factory. Or somewhere else
Sounds like you need a larger alternator, no enough amps for the load
I would look for a battery cable issue such as corrosion or hidden corrosion. Also the grounds need to be checked and cleaned. I have had battery connections that looked perfect, but caused issues.
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