[VetteVet]

One wire alternators don't have the plug on top. It still will charge if the large wire on the back is connected to the battery positive either at the battery or down the line where the external voltage regulator red wire goes with the junction with the cab feed wire. Your truck will not have the horn relay on the engine side of the firewall so they used a soldered junction for the four red wires to connect together. See post 2 above.

Just connect a voltmeter to the back of the alternator and to ground and take the reading. If you get over 13.5 to 15 then it's charging.