An inexpensive $5 -10 Digital Multimeter would do what you need and more. If you're just using it for model railroading, and keep it away from higher voltages, you won't hurt yourself with it, because the voltages and currents involved in model railroading are not dangerous, unless you have a serious heart condition.
Tubular switches and fibre pins are somewhat different than how Fastrack Switches are intended to be isolated. Power to the rails on FasTrack switches is intended to come from the track they're connect to. All that's needed to isolate the internal electronics from track power is removing the jumper, IF power is phased correctly AND the switch is wired correctly internally and externally. There are FasTrack pieces that are designed for electrically isolating sections of track, but this has nothing to do with your switch's issues.
The bad news is that breaking off the pins, will not guarantee electrical isolation, and will probably cause issues with correct normal operation, which will require either replacing the 75 cent (each) pins or always wiring Track power, Aux Power, and Ground to the actual corresponding terminals on that switch, after you figure out which terminals are which, and very possibly not as labeled from the factory.
If you need help using a multi-meter, there are lots of online resources and friendly people here to help.
