I have also used the green knob version battery disconnect on my 59 for a couple of years, kinda ugly with the hood open, but functional. But realistically, a 1999 vehicle shouldn`t have so much computer memory to run the battery dead in 2 months. My 99 F350 stays parked from October thru March or April, and the battery doesn`t go flat. Maybe you have another parasitic draw somewhere. On newer cars, the battery can run down pretty quickly, since they may have 10 or 15 computers that all have some memory function, that sap away battery power, but a 25 year old vehicle shouldn`t do that, IF the battery is good, and has no excessive current draw. although the battery disconnects do work, in most vehicles with digital clocks, radios, etc, you will lose the radio presets, and the clock with be flashing "12.00" every time that you unhook the battery. Not a huge deal, but a bit annoying.