Very illiterate when it comes to wiring. Trying to test the sending unit for fuel gage on an 87 Chevy 4x4 350 tbi. The pump and sending unit are attached together at the top on the outside. How do I test for proper grounding? Trying to find proper wiring for truck after someone cut all wires under the truck for both tanks. Got the pump working just not the gage. Put another gage on it and both are pegged out at full. Any help please..