15 year old house. No other electrical issues known. Plug and switch not used often. Wanted to add an outlet and ran into this problem. Disconnected plug so it can be ruled out. Replaced switch to rule it out, same problem. Switch on: 0v at switch 0v hot-ntrl 120v hot-grnd 120v ntrl-grnd Switch off: 98v at switch 98v hot-ntrl 120 hot-grnd 12v ntrl-grnd Other switches on the circuit measure: 120v hot-ntrl 120v hot-grnd >1v ntrl-grnd They are not effected by the switch. Not sure what to do?