What causes a battery drain in a 1978 kz kawasaki 650?

I can be countless things, but a short is likely if the systems check out otherwise (charging, battery, etc.). To diagnose, you can check the drain on each circuit via the fuse box using a multimeter which can be had for about $10 at radio shack etc.. Buy one, learn to use it (5 minutes max, instructions included). Check charging, battery, then after, if thats all fine, pull fuses and check each circuit, based on fuse ratings, useage indicated by meters, and switching circuit devices on and off. If your battery is old and has gone dead, been stored on the ground, been through cold winters, it's likely just not holding a charge is all. Oh, if battery connections are dirty, the charging system wont be able to refeed the battery. Easy stuff, just gotta start, keep swinging til you figure it out.