Working on a friends' '67 Coronet, about 8 months ago I replaced the original fuel tank with a new stainless tank. I replaced the sending unit several years before with a stainless unit. After trying a 7" ground clamp and then a wire clamped to the outlet tube to the body, the needle only moves about 1/16". I grounded the wire from the sending unit to the body and the gauge goes to full. Also, the fuel line to the pump is stainless.
Is there problem using a stainless tank that should be grounded differently?
Thanks, I hope I covered everything,
Tony