If your megohmmeter is reading "OL" (over load) or "I" (infinity), these are commonly used readings on megohmmeters when the measurement exceeds the maximum indicated value of the tester.
For a successful test, the insulation resistance measurement must be equal to or greater than 1 Gigaohm (1 Gigaohm = 1 G ohms = 1000 Mega ohms = 1000 M ohms). We recommend that you always check the megohmmeter instruction manual as each manufacturer can use different symbols or values for their testers.