My alternator is not charging the battery.
I pulled it and O'Reilly said it had a bad capacitor.
Can the capacitor be tested through the three prong plug or do you need
to tear the alternator apart to get to it?

Also, what is the black part next to the three prong plug?
It is showing an open circuit between the ground and the end of
the wire. The insulation broke off when I removed it to test.

Voltage regulator is good.
I had this alternator rebuilt three years ago locally.

Jeff

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1984 300SD 300,000 miles--two tank WVO setup
2.88 diff & 500SEL anti-squat rear end