Merc alternator not putting out voltage

[speakrdude]

So, a friend has a 94 ish Mercruiser 3.0l and the alternator has quit. I replaced That alternator, 5 or 6 years ago for her, as a gift.
Upon inspection today, I’ve found that on the B+ output lug, there is a black wire that connected to a device like a capacitor maybe, bolted to the alternator exterior. Is that simply a radio Cap to keep static out of your station?
It’s broke loose on this one. Also, this a 4 wire alternator. thanks