oil light on

[dan650plus]

my oil light came on, it was about 1/2 qt.low added oil and light is still on.
runs fine no noise coming from top end of any where. is there a way to check the sending unit to see if it is bad? bike is a 79 GS750EN.

[Nessism]

It's easy to check. The sender/sensor is attached to an oblong plate right under your carbs. Pull off the wire and the light should be off. Ground the contact and the light should come on.

[sedelen]

An oil pressure light could be a serious thing. The oil sending unit is on top of the rear of the crankcase in the middle below the auto cam chain tensioner.
It should have a wire attached to it. Hopefully, it's disconnected and touching your engine case somewhere.
The way it works is there's a little plunger that moves up when oil is being pumped. It is down when your engine isn't running, and when it's down it supplies the ground to the oil pressure light which turns it on. When oil is pumping, the plunger moves up and opens the oil pressure light circuit which turns off your light.
Turn your ignition to on so you get your light, once you verify your light is on, disconnect that wire to your sending unit, it should go out. If it does, it's telling you the circuit to your sending unit is good. If it doesn't you have a short to ground somewhere between the light and the sending unit.
OK, lets say your light goes out when you disconnect your wire, you now either a defective sending unit or your engine isn't pumping oil.
If you remove your sending unit you should be able to move the plunger up and down quite easily. I believe also there's a little flat washer held on with a screw. If all looks normal I would clean it and put it in the bike and
see if the light goes out when started. If it doesn't within a few seconds I would stop the engine immediately. These sending units don't go bad too often, but they do sometimes. I had to replace one my GS1100 for the reason my light wouldn't always come on when I turned on my ignition switch. I would hope that you find the wire that goes to your sending unit grounded against your crankcase and disconnected from your sending unit. I would not run the engine until your certain it is pumping oil.