Fuel sending unit wire

Hi guys, I need some help. I am trying to get my fuel gauge working on my 74 dart. I have taken the instrument panel out and tested the gauge with some AAA batteries and it is fine. I replaced the voltage regulator with a solid state chip, capacitor, and heatsink. The temerature guage does not work either but the rest of the instrument panel lights do, (voltage, illumination, brake, etc.). I tried grounding the wire from the fuel sending unit and turning the switch on and the gauge doesn't move. I traced the wire up from the trunk along the sidewall up to the fuse block. I tried using a test light on the wire at this point while turning the ignition on to see if any power was in the wire and found none (not sure if this is a viable way to testing it, I have a multimeter I could use).

I also found a light purple wire coming from the firewall running under the dash that has gotten hot and lost all it's insulation (was that way when I got the car). It has an aftermarket gage cluster attached under the dash to read water temp and oil pressure. I am thinking that maybe this melted wire is somehow related to the gages not working and therefore they moved to the aftermarket gages.

My question is can anyone point me in the right direction to go from here.

Also if anyone can post a link to a wiring schematic it would be a great help, would love to lose this 5 gal can of gas in the trunk I'm riding around with.

Thanks,
Russell