atnuts

...I installed a tach on my f4i to see what my idle is running at but from the front end slamming down hard from trying circles the needle broke so I bought another one and instead replacing the whole thing(tach and wires) I just cut the wires mid way so I can put male/female ends on to make it easier to replace. but when I cut the wires I heard a fuse 'snap' and the needle on the tach dropped alittle??? The bike was turned off. My question is this, is the tach draining my battery when the bike is turned off and just sitting there? or is this normal? I have the tach crimped to the original wires off the connector.
How can I measure what is actually pulling juice from the battery? need to know before I replace another battery

thanks