First test would be to remove the positive battery terminal(s). Run a bolt through all the terminal rings that you had connected to the positive side of the battery (the stock ones and any accessories you might have connected there) and fit a nut and tighten to clamp all the rings together. Next connect your multimeter (set to measure current) between the clamped positive terminal rings and the battery positive terminal and take a reading with the ignition off. Start with the meter set to read Amps (just in case there is a larger draw) and then fine tune to the 500mA scale after that. DO NOT turn the ignition on with the meter connected or you will risk frying it! [You can remove the main fuse and connect the meter across the fuses terminals to measure the current draw, but this will only give a reading for those components connected through the main fuse (which isn't everything and won't cover any accessories).]

The above will measure the current being drawn by everything on the bike when it's at rest. If there is a spurious current, then the next thing to do is establish which circuit is causing it.

To do this, the easiest way is to (with the ignition off and battery terminals reconnected) remove one fuse at a time and connect the multimeter across the two fuse terminals and get a current reading. Repeat this with each fuse in the fuse box. Don't forget to do the same with any accessories (and their fuses) you have added too. This should tell you exactly what is causing any background current drain.

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