1980 650 LTD blows main fuse

Got a 1980 650 LTD (early enough production that it shares all of the electrical with the 79 SR) that has a short that blows the main fuse. The tail light ONLY works with the ignition switch in the "ACCESSORY" position. The brake light works with the front and rear brakes engaged. With a volt meter I can read 0.09 volts on the frame when the key is in the "ON" position. I've traced it to the right side handle bar switch. If I unplug the gang plug from the main harness I read no voltage on the frame and still have no tail light. Is it safe to assume that it is in fact the right handle bar switch? How does this make the tail light NOT work with the key in the "ON" position?

I'm not very much on the electrical issues, so I was hoping someone could guide me. Thanks for any help you can give.

unplug everything you can and start reconnecting 1 at a time till you narrow it down

That is essentially what I have done, but rather unplug one item at a time, then check for voltage on the frame. If voltage was found, plug that item back in and try the next item.