ground strap on A body to motor??

I now believe in majic jeannies. Found the cure by chance, hooking up some mechanical gauges and a tach. I had a friend Ed who was up for the summer from Florida hook up the electrical power supply and grounds. While he was under the dash he pointed out some bad connectors, plugs and all that electrical stuff I hate and he volunteered to fix 38 years of things that happen while other people own the car before you do. He didnt even like the factory ground so he improved that as well. So job complete, we check for lights and function..double check everything else electrical for function also. All is OK. I notice on the drive home the fuel gauge is now reading I have gas........."Course I'm thinking "Now whats wrong the the fuel gauge". After all we had it pegged as the ignition switch as the problem right? So we stop at Sunoco and filler up. Now the gauge reads FULL. This cant be good right? Sure enuff, the gauge has worked fine since Ed did his thing. Even the E -brake light functions when applied. I can tell you this, {of all the gauges in the car } after not having a fuel gauge that worked for 2 years I cant stop staring at the damn thing