Sn95 and foxbody 5.0 electrical problems and bad grounds.

After chasing a few small electrical problems for a while, I thought I had an overheating problem. Temp gauge was running in the “A” in normal. Thinking I had a head gasket issue, I started noticing troubles with other gauges and charging issues. Alternator was putting out 12.5 or 12.6 volts to the battery at idle and it should’ve been putting out 13.5 or so. Oil pressure gauge was also pegged out high for a long time. Fuel gauge was intermittently erratic. Also didn’t want to start when the engine was hot. Had to be jumped off or pushed off a couple times. I had replaced the temp sending unit and oil pressure sending unit with motorcraft parts. I had the alternator checked at local starter/generator shop and was told it was working perfectly. Dumped lower radiator hose and put 2 bottles of prestone coolant flush and topped off with water. Turned Heater on high and drove 20 miles at the time at 60mph. And flushed it all out with fresh water and replaced with fresh green coolant. Still showed to be running hot. Then eureka!!! I hooked a makeshift ground cable from the negative battery terminal to engine and the gauges read waaaay better. Then I knew I had a bad ground somewhere. Or at least weak grounds.