If you've gone and purchased a multimeter then it should be easy to check the fuse. Remove the fuse, set the meter for resistance, (ohms) and put one lead on either side of the fuse. You should have a very low resistance value and if so, the fuse is good.
If the fuse is good, then you can start looking at voltage beginning at the output of the charger and checking at every connection between there and the battery.
If you can get the wiring diagram of the bike, look it over. Even if you don't have an electrical background, you may learn something that makes it easier to troubleshoot.