I have a 2005 Ford Ranger V6, 3.0 ( i have 2 questions)
I check my oil and I was running on 1.3 Quarts of oil after I measured it.
The oil light works but it never gave my an indication the oil was that low.
No engine knocking, no over heating.

I later changed the oil filter and added 5 quarts of oil. Truck appear to be running great.
Did I cause any damage to my engine running on under 2 quarts of oil?
How low do the level have to be before the oil light come on?

 

If there was no oil light, then there was still pressure, even if it was low.
I wouldn't worry about it.

The red light doesn't indicate low oil level, at least on my 99, it's for pressure only.
Red light means no pressure.

 

Best check is to pull the Camshaft Synchronizer and check wear on the gear. The oil pressure light is controlled by a switch, >5psi is considered good. Switch triggers below 5psi. The problem is oil pressure rises with RPM.