gauging it

[Northern lights]

My truck is a 64. The PO chose to forgo the factory gauges in favour of some aftermarket ones mouted under the dash. I want to hook up the factory gauges so I can remove the underdash ones but have never been one for electrical issues so I need some help with how they should be connected. The aftermarket temp gauge uses a probe so I will need to replace thet with a sending unit, that's fine, but the factory gauge has 2 terminals that I assume are one to the SU and the other to ground. If so, which is which?. The Batt gauge also has 2 terminals but is this a volt or amp gauge?. does it matter?. The plugs are wired into a harness and go ????? somewhere. I don't LIKE to leave unused wire in the harness but, unless there is a way to trace where they go, I will have to just run fresh wires from the gauges to there respective destinations. Any help would be greatly appreciated. The oil gauge is OK, it's mechanical

Thanks
C