I swapped my 1979 out to guages from idiot lights and added a factory midship fuel tank. Find a truck same year and pull the entire harness with altenator wires, tag everything and swap. You will need to change your oil for sure and maybe temp sending units on the engine. I changed out fuse box with new fuses and cleaned all connections on plugs and fuse box. It took me about 3 hrs to pull and label the new old harness. about 2hrs to clean all contact surfaces and 6hrs to pull old and install new used harness it included a factory fuel switch on the heater control unit, every thing was a label and plug and play, it works great. I would also clean all grounds like fire wall to block ect.. I added a ground from the block neg battery cable to the frame and a cab to frame and a bed to frame ground, this is very improtant and will help ensure proper gauge function. good luck.