Wiring Question for Modern Clock Co Radio Ad Clock

Discussion in 'Electric Horology' started by wbranko, Jun 6, 2017.

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  1. wbranko

    wbranko Registered User
    NAWCC Member

    Feb 1, 2004
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    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 sad0116.gif .

    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?

  2. THTanner

    THTanner Registered User
    NAWCC Member Donor

    Jul 3, 2016
    Carson City, Nevada
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    A picture would help, but if I were doing this I would switch the power feed (black wire I assume - unless someone has wired it wrong along the way) that goes to the ballast. That way you avoid the ballast hum, don't waste electricity keeping the ballast powered, and avoid the possible issues of hitting the ballast and the bulb with a surge if you were to switch just the bulb and leave the ballast hot. Most modern ballasts and bulbs can take that surge for awhile, but it can also damage both of them in some cases. Also, if you switch the power feed to the ballast, turning it on will allow the ballast and bulb to go through the standard startup and warm up as designed.

  3. wbranko

    wbranko Registered User
    NAWCC Member

    Feb 1, 2004
    Country Flag:

    First of all...thank you. This definitely answered my question. I'll post some photos...but this is the ORIGINAL wiring of the clock. According to the clock motor, this is April 1958! Consequently, the color coding is...well...pretty much non-existant. I have a new ballast to replace the old original ballast, and it has the same color code you mentioned. I have figured out which wires go where, so I'm pretty confident I can get this right. I will try to post some photos of the new wiring when I get it done in a couple of days.

    Thanks again!

    306998.jpg 306999.jpg

    Attached Files:

  4. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
    Calif. USA
    Looking at the ballast, the block wire would be where
    the switch would go.
    You should use a polarized plug with the black going to the hot
    socket lead.
    Don't confuse the ballast blue with the motor blue leads.
    One of the whitish leads from the ballast is really the blue
    ballast lead.
    Tinker Dwight
  5. James McDermaid

    James McDermaid Registered User
    NAWCC Member

    Apr 29, 2011
    looks rather simple as the wiring diagram for the light part is printed on the ballast.

    The clock motor would get 120 volts AC all the time so the clock stays running.

    Since the power cord is probably not a grounding type it really doesn't matter which side you wire in the switch but I would probably wire in the black wire side.


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