99 GT project, headaches

[LittleYellowGT]

I've acquired a 99 GT (4.6L w/ 4R70W). It's got 120,000 miles on it. It had a lot of electrical gremlins under the hood. I've re-wired just about everything under the hood. New elec plugs, new alternator, new coils, new starter, re-did all grounding connections, etc. Front end electrical seems solid now. But... the electrical charging light (dash light) still comes on and goes off "randomly." It appears to be associated with the fuel tank / system. If the tank is full the light stays on constantly. Between 1/4 and 3/4 full the light is always off. Below 1/4 the light will flicker when I hit a bump, swerve back and forth the light goes on and off. Below 1/8 of a tank the light stays on...
It appears to be associated with the fuel pump / float, but before I go digging into the fuel tank and replacing stuff, has anyone ever seen this before?

 

[wmburns]

If this were my car I would be thinking "bad/weak cluster ground". Or thinking printed circuit foil trace repair.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

Recommend confirming the ability of the cluster ground to carry a current. Use a test light that will "load" the circuit. This confirms the ability to carry a current. Test the black wires and the black wires with a white stripe.

Here's some more information that may help.

Cluster PC foil trace repair
https://www.allfordmustangs.com/forums/v6-tech/304608-my-odometer-goes-off.html#2657361