Check gauge light flickering

[Tbruz]

A mechanical gauage was isntalled on the manifold( in place of the OP sending unit) ; reads 47 lbs at first start, around 1000 RPM.
Mech gauage responds similarly to dash gauge, i.e higher pressure with higher revs, lower pressure at idle or warm.
Based on this test I beleive the Oil Pump is fine and the gauge is reading correctly.
Changed out Oil filter to a WIX and changed oil again ensuring its quality 5w/30w and at the correct level.

Same thing happening, cold start, no light for 1 second at initial start.
then 1 to 2 seconds after started the check gauge light comes on for around 60 seconds.
New data point is that if truck is left to get stone cold (say 12 hours later) same thing happens, No light for 1 to 2 seconds followed by up to 60 seconds of Check Gauge light.

Dash itself, OP sender and 2 Temp senders already ruled out in earlier tests.

Where to next ??
Grounds? If so where are they.
Individual wires? which ones
PCM?

Thanks for any input
Tbruz

 

[SunlitComet]

there are two ground wires you can check for resistance. remove the cluster and pull the connector from dash slightly. black/white and black measure the resistance all the way to the battery looking for anything unusual along the entire path and you can narrow further from there. other then that that and assuming you have a good 13+volts on your gauge, showing that good voltage is reaching the cluster on the two pink wires from separate fuses(one really does not have a role in this light at all btw), that leaves me a bit stumped at the moment.

 

[Tbruz]

Problem Solved and verified at this mornings 1st start; no more Check Gauges light.

Vehicle was brought to my mechanic who re-validated that all senders, oil level,oil quality, mech reading of Oil Pressure were in fact correct. On the recommendation to check wiring, the ignition switch wiring was pursued. They measured a voltage difference in a wire pre-start, post start(under 60 seconds) and post start(over 60 seconds)
R&R'd ignition switch harness and Problem is solved!
Thanks
Tbruz

 

[SunlitComet]

which wire please?

 

[Tbruz]

I wasn't there but I'll try to get specific wire details.

Per the mechanic, it was the feed side of the transmission fuse in the interior fuse block.

I do know they had hooked up their remote start controls and noted that when they remote started the vehicle there was no CG light versus a start with key in; CG light on for around 60 seconds.
Tbruz