locost_adam wrote:
my fuel gauge reads full - ign on or off.
if I disconnect the ground at the sender the gauge drops to empty.
This sounds like a mis-wire to me rather than a "bad" ground. With your ignition off, you should have no current through the meter circuit. Since the gauge changes when you pull the ground at the sender, you DO have current in the circuit. Time to check the wiring diagram and buzz out the wires.
By the way, is the sender a Miata sender or an after-market unit? How about the wiring harness - Miata or after-market (or custom?) If you have a sender/pump (in tank) combo unit, does the pump run OK?
You do know that there are at least four and maybe many more completely different gauge/sender circuit designs used in the most popular cars and after-market solutions, right?
John