1983 KZ750N Spectre oil light comes on when I rev the engine.

I would still guess that the sensor is at fault, but it could also be the warner unit. Don't know for sure how to confirm this without swapping them out with new/working ones.

If I'm right and the sensor actually closes the circuit when there is enough oil (meaning the warner unit detects a closed circuit and turns the light off), the light should go off when you ground the lead that goes to the sensor (unplug the sensor and connect the lead going to it to the engine or battery -ve). If this stops the light from coming on when you rev the bike then the sensor is probably faulty - I would assume it works for extreme cases (full or no oil) but in between it is not reading properly. If you still see the light coming on when revving, then the sensor can't be the problem and it's probably the warner unit.

Oh okay. I’ll see if I can buy a new sensor. You mentioned a warner unit. Where is that? Is that different than the sensor?

Thanks!

I bought a new sensor and I just tested it the way you mentioned. The light stays on when you ground out the wire or unplug it. For now I’ll just keep an eye on the oil level through the site glass and ride around.

Thanks!

In some old KZR topics. some guys installed an oil pressure switch, but you'd probably have to drill & tap some threads.
From EB pics the 750 Spectre crankcase appears to have the provision for installing an oil pressure switch under the RH engine cover. same location as the 650/750 models. Then you could probably eliminate the oil level sensor altogether by replacing the oil pan.
(note: I'm not certain if the pressure switch oil passage has been machined, though)

... 1981 KZ650-CSR.

You are correct. It isn’t machined. But, I was just riding and noticed that as the bike warms up the light stays off until I really get on it I mean in the red line. So I’m not sure why it’s doing that.

Also the headers are smoking a lot I know it’s from the oil that spilled all over it from the top end blowing. Does anyone know how long it will take for the smoke to go away?

Interesting that the light stays on when grounded. [strike]That means that the switch probably works as I first thought - grounds the connecting wire when the level is low. Not sure why the light would stay on when disconnected - there must be some way to detect if the circuit is broken or if the switch is just open. Without knowing how the switch works it would be hard to say.[/strike] total nonsense see next post.

Did the new switch work up to the redline?
Also, I'd recheck the oil after the bikes been on it's side - sounds like you've burnt through a bit of it. I think I'll stick to just draining the oil for this sort of work

Not sure where the warner unit is, just skimmed the pages in the manual that mention it.

Reading the manual again I see that the switch is closed (< 0.5 Ohm resistance) when the oil level is OK. This makes sense - when the connecting wire is grounded the warner unit will detect this and switch the light off. Wondering why it would stay on when you ground the wire - that should be basically telling the warning system there is enough oil. Anyone know how this works?

When the new oil sensor comes in I’ll install it and let you know

I’m currently still having trouble with this light coming on. Any ideas? Should I buy a new sensor or warner unit?