fuel and temp gauge not working, melted wire on printed circuit board

[vettedad61]

on my 1972 C10 it has factory gauges and tachometer.

1) when I bought the truck the printed circuit had a melted wire that serves the fuel and temp gauge.

2) I recently did a full restoration of the entire truck, I bought a brand new factory correct harness, new printed circuit board for the gauge cluster, new temp sending unit, new fuel sending unit, etc. the gauges were not replaced.

3) the same wire on the printed circuit behind the cluster melted that serves the fuel and temp gauge.

Can anyone tell me why? or what steps I need to take to fix this?

Thank you!