hi C,
Welcome to AAC.
Have you considered a Wheatstone bridge of say 420K as a starting point.?
E
I might help if you can tell us how you ban intend to use it.
hi C,
Will the 420k's in the socket being tested have any voltage across the 420k as part of a working circuit.?
E
hi C,
So a Bridge, made up of say one 420K and the other half of the bridge say 10k's, a AD623 INA [ OPA] driving a transistor LED or Buzzer, powered from say a 9V battery could work.
Make the circuit detect a Zero balance .
E
Update:
Is it always going to be 420K, also what resistance tolerance is acceptable.?
hi C,
Check out my update , post #8, there maybe a cheaper , simpler way.
E
For a Go/NoGo circuit a 470k half bridge and a window comparator with adjustable upper and lower trim pots. No need to read and think.
? wiki shows 470k one ? https://en.wikipedia.org/wiki/British_telephone_socket#Making_the_connections