Weird Electrical Gremlin. non-P-car related

[Looking_for_911]

Ok guys and gals,

I've got a weird electrical gremlin on my daily driver, the Volvo 240D that I'd like to run by you.

A few weeks ago on an intermitent basis, the oil light (aka Idiot Light) started coming on......
When the engine is not running.
Car has oil and light goes off when you start her up. Stop the engine and the light comes on all the time now.
My Volvo mechanic - whom is a great one - hasn't had this come his way and is scratching his head over it.

Any ideas form the Pelican Brain Trust?

Thanks,

JR

[HawgRyder]

For starters....the oil light is in a series circuit.
The power comes from the battery (through the ignition switch) to the top of the oil light....then the oil sensor (on the engine) is a normally closed switch (meaning short circuit)...as the oil pressure rises, the switch opens and the oil light goes off.
Now...if power is somehow getting to the oil light...short under dash, crossed wires, previous owner trying to install radio, alarm system, sex lights under dash, etc,,....it will bypass the ignition switch and power the light.
The possibility of this is remote..because if the power was at the light...it would also be at the ignition system (bypassing the key switch).
I would be looking for a change in wiring under the dash or in the engine compartment where the normally grounding circuit of the oil sensor is now being powered by the mistake.
In this situation, the light would come on if the key were turned off (grounding the top of the light instead of the bottom).
How's that for a start?
Good luck
Bob

[Looking_for_911]

Originally Posted by HawgRyder

For starters....the oil light is in a series circuit.
The power comes from the battery (through the ignition switch) to the top of the oil light....then the oil sensor (on the engine) is a normally closed switch (meaning short circuit)...as the oil pressure rises, the switch opens and the oil light goes off.
Now...if power is somehow getting to the oil light...short under dash, crossed wires, previous owner trying to install radio, alarm system, sex lights under dash, etc,,....it will bypass the ignition switch and power the light.
The possibility of this is remote..because if the power was at the light...it would also be at the ignition system (bypassing the key switch).
I would be looking for a change in wiring under the dash or in the engine compartment where the normally grounding circuit of the oil sensor is now being powered by the mistake.
In this situation, the light would come on if the key were turned off (grounding the top of the light instead of the bottom).
How's that for a start?
Good luck
Bob

Bob,
Thanks for that very good start!
Embarassing though it is because my grandfather and great-grandfather were industrial electricians! I should have taken up the trade.
They're rolling in the gorund right about now!
Thanks again,
Jeff