If you have an ohmmeter, check between the Red and Red/Slate leads for a resistance of 2650 ohms, and between the Black and Slate leads for a resistance of 1000 ohms. There should be no continuity between any other combination of leads.
You can buy an adequate digital volt-ohm meter on Amazon or other on-line sources for twelve bucks.
meter That type of ringer is notorious for just dying without warning. They were used in smaller phones, like Trimlines® and other later phones. I suggest that you get a C4A which will outlive you. Want me to send you one?
Or you could use a Sonalert® (piezoelectric buzzer) in series with a .5 mFd capacitor, both available at Radio Shaft.
