Aluminum Fuel Tank Project / EFI Fuel Cooling

Do I understand that the main block ground is hooked to a fuel pump bolt? So I'm guessing you have a 1/0, etc from there to the chassis for engine starting? I doubt that alternator grounding is the issue.

That's easy to prove. Get some scrap wire, anything, no16 or even larger, long enough to reach from the battery to the alternator. Make up a battery clip on the scrap wire and hook that to your rear ground. Run the wire up front, hook one probe of your voltmeter to the scrap wire, and the other probe to the alternator case / ground with the meter on low volts.

Check the reading first with engine running to simulate "medium cruise" with battery up and normal, then check again with whatever you can load it--headlights, heater, etc.

You are hoping for a really low reading, less than .3V would be good.

What if anything are you doing for a batt. disconnect?