105 to 145 amp alternator swap

[VorTecxas]

I have a 1996 1500 Sierra, 350. The 105 amp and 145 amp alternators use different plugs, and I have already got the harness for the 145. My question is - though there are 4 ports on each respective plug (and 4 wires coming from the new harness), there is only one wire coming from the current plug (which I assume is for the voltmeter, since the one bolted to the rear is the outlet to the battery). Do I need to run any of the other three from the new plug to anything? And which one from the new plug do I splice into the single wire?

[Chris]

Usually one runs down to the terminal on the starter where the battery connects. And that's how baby's are born. I mean how it charges the battle. I think one may be a ground too