Quoted from PinballManiac40:
Better to test the diode in the circuit with the coil. You'll end up doing it at the end anyway.
A shorted transistor to ground, still will not affect the coil resistance measurement either. I even jumpered a coil to ground braid last night and the coil resistance measured the same, grounded or not. Worked just as I expected.
Who said anything about a shorted transistor affecting measurement? I said shorted diode. A shorted diode directly shunts across the 50V and ground lugs of a coil and you would read 0 resistance. You need to lift the connector to both check the diode (otherwise, the diode test will fail across the resistance of the coil), and you need to lift the connector to test the coil in case the diode is shorted. Two tests, one connector lift.
Especially not sure what you meant by "Better to test the diode in circuit with the coil". You can't do that. You always have to lift one leg of the diode off the coil to test. Since these diodes are on the board, you do that by removing the connector. The low impedance of the coil in parallel with the diode will fail the diode test everytime. Instead of reading .6V one way, you'll read ~.1V both ways.