Electrical issues. Batteries

Sounds typical of bad connections. They will show up best when you're trying to pass current through them, so turn on the head lights, then grab a test light or inexpensive digital voltmeter and start at the posts on one battery and test for 12 volts. Move the probes from the posts to the cable clamps, to the body, and to the next place down the line until you find the spot where the voltage disappears or goes real low. That's where the bad connection will be found. Don't overlook the positive cable where it might be bolted to an under-hood fuse box.

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