Electric Oil Pressure Gage Problem

[miked]

Just installed an electric oil pressure gage Circuit Brand (black faced) OEG-12V paired with a Torica OU-101 12V oil pressure sending unit.

Gage reading sweep from 0-10 kg/square meter:
0-2 start
2-6 normal range
6-8 check
8-10 over pressure range

Oil pressure sensor have one terminal only (not the floating type)

I wired the gage terminals given the following using 18 AWG wire:
S - wired to oil pressure sender terminal
G - wired to a body ground within the dashboard
I - wired to a 12V source on the ignition switch when switch is ON.

Now, the problem is:
Gage reading initially was 6 kg/sqcm. Revved the engine and the needle would go down to 3 or 2 kg/sqcm. Upon release of the pedal (decreasing rpm), pressure reading would rise near the max reading of 10 then goes back to 6 kg/sqcm.

after some warmup, gage reading was at 8 kg/sqcm. Revved the engine and the needle would go down to 6 or 4 kg/sqcm. Upon release of the pedal, needle would shoot past the max gage reading of 10 kg/sqcm then go back to 8 kg/sqcm.

as per my knowledge and experience with mechanical oil pressure gages, oil pressure would rise when engine is revved. idle oil pressure is 0.7 kg/sqcm (10 psi). but my electric gage behaves the other way around.

did i miss something? please help. maybe sensor is not compatible with the gage but it's still a guess.

any input or comments is highly appreciated.

[miked]

did some testing lately:

Oil Pressure Sensor resistance is 55 ohms even when engine is revved but voltage varies from 4.12 - 9 volts.

Gage voltage with Key ON, Engine Off:
S - G : 8.4 volts
S - I : 4.5 volts
I - G : 12.5 volts
gage reading is beyond the maximum. same effect when the sender terminal is shorted to ground

Resistance tests (all readings in ohms):
With G connected, I disconnected, S connected:
S-I: 101
S-G: 44
I-G: 145

With G connected, S & I disconnected:
S-I: 101
S-G: infinite
I-G: infinite

With G connected, I disconnected, S shorted:
S-I: 101
S-G: 0
I-G: 101

With G disconnected, I disconnected, S shorted:
S-I: 101
S-G: infinite
I-G: infinite

With all terminals disconnected:
S-I: 101
S-G: infinite
I-G: infinite

Last night, oil pressure ay lumalampas sa maximum kapag nagdedecelerate ang engine.
sorry too long at siguro medyo confusing. hope somebody can relate. tia