It sounds like you have a broken ground. Possibly in combination with something else that is feeding power directly to ground in proximity to what your gauge is grounded to.
The first thing I would do to rule this out is to undo the ground for the gauge and run a jumper ground directly to the battery terminal. If you're already grounded at the battery post, I'd say the fault is internal to the gauge or that the sense wire or sender is bad.
Did your pressure sender come with the kit?
The first thing I would do to rule this out is to undo the ground for the gauge and run a jumper ground directly to the battery terminal. If you're already grounded at the battery post, I'd say the fault is internal to the gauge or that the sense wire or sender is bad.
Did your pressure sender come with the kit?
Wait, did the gauge come with a sending unit? Pretty sure you cannot use the one that is on the car or that comes from a parts house that is an OEM replacement with many if any of the aftermarket electric gauges.
Troofs... a good portion of them are [switches] and not sending units. Having a switch can def cause the needle to peg high/low.
I think @Mustang5L5 has some part numbers to distinguish the two?