battery keeps goin' south?

[BUXMAN66]

yeah,i got a wierd one for you electrical guru's out there! so any hoo,i buy me a nice tach. get it installed,run my lines to -1).ground on the body.2).light - to my headlight switch. 3).line to my hei dist. 4).power lead to switched power-key on. so how come everything works fine and dandy when on but something keeps killing my brand new interstate battery? when you push in on the lights it correctly turns off the light in the tach.,so there's no power drain there.obviously,when you turn off the ignition the rpm's go back down to "0".i have never had problems with the battery being dead after a couple of days until i hooked up the light to the tach. would there happen to be some kinda diode or something that is causing a slow ,trickle draw?checked the condition of my alternator by removing my positive battery cable, and the engine continued to run.would a bad voltage regulator do this?i have currently the old style external voltage reg. (was a good reason to go buy a 1 wire chrome 100 amp.,waiting on ups to bring it!) thanks for any help