Wierd oil pressure light issue

[jseabolt]

Just noticed this as I was waiting on my garage door to open.

On my 131. Oil pressure light flickers dim with headlights on. Turn the
headlights off and it quits flickering.

However at idle put the car in drive and the oil pressure light burns bright.
Put the car in park and it goes off. The engine speed does drop a little bit
when the car is in drive but it doesn?t drop that much. In fact the idle screw
is backed all the way out and the engine still idles too fast (like 1500 rpms).

Sounds like either the switch is going bad or some sort of grounding issue
with the switch but the oil pressure light switch is grounded through the
engine block, not a common ground connection like the park and headlights are.
Or perhaps something in the instrument cluster.

First time I have ever noticed this. Coming home from work, I did not notice
the light burning at all. It seems to have started when I pulled into my
driveway. I?m going to swap out sensors and run an extra ground cable from the engine to the body and see what happens.

I'm not going to drive the car until I verify it does have oil pressure but I
doubt I have an oil pressure issue.

Anyone ever seen this?

[Tas131]

With headlights on and oil light flickering, does it change with engine revs? When light comes on with trans in drive, does it go out if you raise the revs? If you suspect an earth issue, check the main cable from block to chassis.

[jseabolt]

Finally got around to digging deeper into this. Originally I thought this was some electrical glitch but I believe now it?s in the switch.

The problem occurs when the engine temperature is at normal operating temperature and in gear. In neutral or park, it goes away (rpms increase).

So I swapped out an oil pressure light switch from a spare Yugo engine. No difference.

Then I changed out the 10W-30 oil and Fram oil filter for Shell Rotella 15W40 and a Purolator oil filter. No difference.

So I connected an oil pressure gauge. Here are my readings:

Cold idle: 60 PSI
190F : In gear 15 PSI. In Park or neutral 20 PSI.

There is no tach on this car being an automatic so I don't know how many RPMs the engine increases when I put the transmission in park.

So the switch is closing somewhere below 20 PSI. Based on what I've read this switch should kick on below 10 PSI. Anybody know at what
Pressure this switch is supposed to kick on at?

Based on what I have read 15 PSI at idle is OK and won?t cause any engine damage. But the light annoys me. I?m going to substitute a switch From a Chevrolet and see if it trips at a lower pressure.