Some senders are internally grounded , some are not. I would ground the other wire.
check the back of the gauge that there is 12 volts to the power side.
quite often if there is no oil pressure, and it has hydraulic lifters you will here it a mile away rattlling the lifters.
first off i would check a 12 volts at the back of the gauge, then earth the sender wire, see if the gauge moves.
All this can be done without starting the engine.
if still no good, you could pull the sender out and crank it to see if oil spurts out. I would be extremely surprised if the engine had no oil pressure as the pump drives off the dizzy, and it's the dizzy gear that goes first, which would not let the motor fire up.
hope that helps.
p.s check the oil level !!
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