only comes on after the engine is warmed up- and even then, it goes off and on rapidly, almost seems like it's related to movement but not entirely.

I still don't know why you you said that you checked the oil level by draining it. Is the dipstick missing?

I have a hard time getting an accurate reading from it so I wanted to play it safe

So, the oil light does not illuminate when the key is on and engine off? If the engine is off there is no oil pressure, the light should be on.

Some folks just enjoy an array of analog gauges I'd venture.
For a street-able automobile though, an oil pressure circuit would be better served with a 'transducer'(?) sort of sending system, instead of a leak-prone plasti-line snaking into the cabin area.
What I'm suggesting is quite a bit more expensive, and the 'engine side' sensor/sending unit -is- sort of sizable, and would need to be remotely plumbed & mounted.
When you're working with an engine compartment as cramped as these, I'd advise sticking with a factory signaling light though.

Like these ?

https://a.co/d/3RAkFnm

That's the stuff
That sort of sending unit & gauge style tends to be quite accurate if you can get it adequately plumbed.