I assume you are talking electronic limit switches? You can get 2 wire or 3 wire AC or DC.
The 3 wire are generally used for a load such as a relay etc, 2 wire have lower current capacity and can be used for PLC inputs etc.
The 3 DC wire can be N.O. or N.C. NPN or PNP.
Not a really conclusive test to use a ohm meter, except test for short circuit maybe.
The link shows various types.