With bike running, head light works great on high and low beam but the tail light was burnt out. If i hook up my test light on one of the taillight leads it comes on and on the other lead the brake light works through my test light, thinking to myself this is a good thing. When I put a new 6V bulb in the head light goes out and nothing works, as soon as I pull out the new taillight my head light comes back on...any ideas?

Bad ground at or after the tail light socket

I am having similar issues with theTS. Quite often an earth issue, as already said. Sometimes the 2 lights are meant to be on different circuits and the extra current draw does this. Is the ty an after market fitted kit to make it road legal with no battery?

Sounds like its shorting out when the bulb is placed in, i would strip the light down and see what the wires are like behind the 2 contacts.

TTB