a few basic steps for using a multimeter
Whether you use one every day or rarely, there are a few things you have to do to use a multimeter to troubleshoot your problem:
1. Consider safety before you start. Except for the spark plug wires, there are no hazardous voltages normally present on a bike. But if the engine is running and the regulator is bad, the alternator can generate enough to give you a nasty shock. A more likely problem is letting a test lead slip and short out a hot wire to ground. This can do anything from blowing a fuse to melting a harness. You can make a fine spot welder with a battery and a dead short. Keep your hands on the plastic parts of the probes and watch where you're sticking things.
2. Make sure the meter is set right..DC volts (sometimes they use wavy lines to represent AC and a straight line symbol for DC). If you have a choice of ranges, set it for 20 volts, or the next higher available.
3. Normally there is a black test lead; it plugs into the jack marked COM or GND or with a minus sign. Sometimes there's a choice of jacks for the other lead; you want the one marked V or DCV.
4. 99% of needed measurements are voltage with respect to ground. Connect the black probe to a ground point - the battery neg is best, followed by bare metal on the frame. Remember that with a little corrosion, the battery NEG and frame might not be at the same voltage - a problem that needs fixing before you go on. Check the meter by measuring the battery +; it should read 11.5-13 volts not running. With the lights on check the voltage between frame and the battery NEG; it should be under .25v
5. Sometimes getting at the point you want to measure is a challenge. An old dentist's probe with tape wrapped around the handle can get to where you can't reach with bigger probes. When I get desperate I shove a sewing pin through the insulation on a wire to get a reading, and then tape the wire afterward. But always, think safety and don't let things short together.
Hope this wasn't too basic or long winded. Good luck with the horns.