I am restoring a Modern Clock Company Radio Advertising clock. The way the clock is currently wired, when it is plugged in both the clock and the light come on. The light is a fluorescent fixture not neon . I want to add an on/off switch for the light. I have purchased a period repro rotary switch with two leads that will be installed on the outer can of the clock. I see that the plug leads go one each to the clock motor. One also has a lead to the ballast (black wire). The other has a lead to the ballast (white wire) and to the fluorescent plug. So I see three places I could put the switch...the black ballast wire, the white ballast wire, and the fluorescent plug wire. My question is which wire should the switch be placed into to control the light on/off? Thanks!