Electrical Can't get my SW oil pressure gauge to work properly.

[evintho]

It's a brand new Stewart Warner Wings electric oil pressure gauge. When I turn the key to 'on' it stays at zero but as soon as I hit 'start' the gauge pegs at 80 psi and stays there. However, after I start it once, then shut it off, if I turn it to 'on' again then it pegs at 80. If I let it sit an hour then go back and try again when I turn it to 'on' then it stays at zero. Very strange!
I removed the SW and installed a cheap, brand new, mechanical gauge and oil press shoots to 62 at start up then drops to 50 after a minute or two. So I have the proper pressure. I've replaced the factory electric sending unit with an Echlin piece from NAPA. I installed a new wire. I even sent the SW gauge back to Summit and they sent me another one. All 3 components in the circuit are new and it still does the same thing.
There're 3 terminals on the back of the gauge. 'G' goes to a dedicated ground, 'S' goes to the sending unit and 'I' goes directly to the 'IGN' terminal on the back of the ignition switch.
Drivetrain and harness from a '93.

I'm at a loss! Any ideas?

 

[Noobz347]

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?

 

[evintho]

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 gauge, sender and wire are new. I'll look into the ground issue and report back tomorrow.

 

[General karthief]

Is your temp gauge electic?

 

[evintho]

Is your temp gauge electic?

Yes it is but it's not hooked up yet.

 

[General karthief]

Where is it grounded?

 

[AeroCoupe]

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.

 

[Noobz347]

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?

 

[evintho]

Grounded the gauge to the NEG batt post.....no joy.
The gauge didn't come with a sending unit and there was no mention of that when I called Summit and requested a replacement gauge. Here's the gauge link......

https://www.summitracing.com/parts/sww-82474/year/1993/make/ford/model/mustang#required

Now when I scroll down, what do I find....
Required parts. SW replacement sender! Another $60. I'm thoroughly annoyed!!

 

[Noobz347]