Painless wire, temp gauge help

[GMC3]

I have a painless wiring kit I installed on my truck. Replaced temp gauge that was not working. I have 2 wires in the kit for temperature. One is for the gauge and one is for the lights. Do I need both or just the one for the gauge. Also I have a 350 w/ vortec heads and edelbrock performer rpm intake. the rad hose covers inlet in intake for sending unit and the threads for the stock 1970 are too big for the vortec heads any info on how to hook this up would be helpful. also where can i get the plug that goes into the sending unit to hook up to my wire from painless