Great. Multimeter excellent!
Used it much?
You want either ohms or continuity. Easy if it's got a buzzer.
Pull the Mag switch out. Know how to do that?
The switch should be in the on position when you pull it out.
So there should be continuity/buzz/very low ohms when mm probe connected on the spring on the rear of the switch , other probe on the little brass nut on the bulb post.
That is the +ve connection from battery to bub. With switch in off position, connection is broken , no buzz.
-ve connection is via the metal piece on the bottom of the switch.
Rare that that will fail - it is a permanent connection - ie the switch does not break that connection.
Might have stated some obvious stuff here? No harm.
You can use mm in volts position to test if volts are getting to the bulb.
Easier to make a mistake though.