I recently changed mine to black VDO units and I refereed to my wiring diagram many times. It shows which color goes where and from that you can see what you do and do not need (you will lose the "low fuel" indicator in the conversion). I highly recommend getting a diagram for your year from any of the vendors. But from what I can remember, there is a pink positive wire that loops to all the gauges, I had to split some of the ground wires into two to give the bulbs a ground since the new gauges have plastic cases, the fuel sender is the white/black, the temp sender is the red/black, but don't hold me to it. If you need it for reference there is a photo of the back of the stock gauges on Chuck Melton's site at:
http://www.espotmarket.com/pantera/Electrical_Gremlins/Gauge_Panelc.jpg Let me know if I can help further.
-Richard
'71 #1731