Oil Light Issue

[Omni]

Good Afternoon and Happy Mothers Day

A gremlin has decided to give me something to do.
The oil light comes on but the mechanical pressure gauge shows anywhere from 20 to 60 lbs depending on if the motor is idling or cruising down the road. Once on, it stays on.
The car is a '65 Newport 383 2V. the crankcase if full. The oil (Shaffers 10W30) is about 6 months old. The filter (Wix) is also 6 months old. The motor was overhauled two years ago (Rings rods main bearings replaced along with the oil pump.) A windage tray was also added. The mechanical gauge is plumbed to the 1/8" port that the sending unit occupied. The sending unit is in the 1/4" port on the opposite side of the block. It has been plumbed that way for 2 years with no issues (so I thought). No disagreeable engine noises, but it is unnerving driving with a bright red warning light starring at you. I changed out the sending unit for an NOS Standard Blue Steak unit earlier this week. No issues with the couple of short trips. Today, on the way home from church, (18 miles) the light came to life again.
Any thought/suggestions are welcomed.
Thanks for your time
Omni

 

[Big_John]

Assuming the mechanical gauge is reading correctly, it comes down to a couple things.

First is if the wire from the sender is shorting to ground somewhere. That could be a break in the insulation or something like that. The other cause could be the sender itself. They are a real simple part that works, but it can still fail. So... Look at the wiring from the sender first and if it's OK, I'd try replacing the sender. A new sender is under $10.

 

[Omni]

The gremlin has been exorcised.
The FSM write-up indicated that a gauge tester is needed, but at the end of paragraph it indicated that a cause could be a shorted or BROKEN Wire.
The wiring schematic showed that the wire (gray) terminated in the top plug of the bulkhead connector.
As it didn't make any difference whether or not the wire was attached to the sender (the light stayed on either way) I would check the continuity from the connector to the sending unit.
With trouble light in hand, I was going to disconnect the connector from the bulk head when it noticed that it was not securely attached to the clips. The 'loose' side was the same end as the gray wire to the sender. A long flat bladed screwdriver gave the extra pressure needed to 'snap' it back in to place.
With the connector now secured the oil light is off.
I was preparing myself for a possible trip into the wiring world under the dash.
Another case of starting with the simple stuff first.
The connector apparently has been 'unsecured' for a couple of years (when the motor was out). It just took this long to cause problems.
Thank you Big_John for the response.
Omni