I want to wire a separate power on indicator light to the ON side of an existing light switch. I'm familiar with how to wire it. The mini light I'm using is rated for 110v and has two extremely small gage pre attached wires. My question is can I connect the small gage wire to existing 12/2 and not cause an issue. I realize there are light switches that have this feature. However, they are not the solution for this application. Please read the below:

My barn has no windows and when the door is closed you cannot tell if the lights were left on. The indicator light would mounted outside so it's visible . The question is will it be safe to connect the small wire gage to 12/2. Yes I could add an outside light. However there are four other separate light circuits and a fan that I wired. Don't want the barn to look like lamps are us. That's the reason for a small light.

  • Your question isn't clear. What exactly is your plan? Please revise to explain more clearly how you intend to make the connections, or provide a diagram.
    – isherwood
    Mar 22 at 21:02
  • And why wouldn't you just wire the indicator lights to the switch in parallel with the primary lights? What's the reasoning behind bringing in a second circuit?
    – isherwood
    Mar 22 at 21:05
  • 2
    If you want to mount a light outside your barn to show if the inside lights are on, why does it have to be a special "indicator" light with special sketchy wires? Why not just buy an exterior sconce from a large cheap hardware store, cable it in the normal way and put a 3W LED bulb in it? Or even, put an 11W bulb in it to light up the entrance and double as an indicator?
    – jay613
    Mar 23 at 14:04
  • 1
    Drill a hole in the door or wall, cover it with a clear plastic cover and weatherseal it up.
    – Huesmann
    Mar 23 at 15:04
  • 2
    @Huesmann that's a long winded way of saying "Install a window". :)
    – FreeMan
    Mar 23 at 16:18

3 Answers 3


Instead of a "pilot light", simply install a UL-approved decorative "carriage" light near the door or a big ugly "security" light to the top of the barn or anything in between and wire it into the existing switch.

With this going on/off with the interior lights, you'll never wonder whether the lights inside are on or off, or not be able to tell because there's heavy rain and you can't see the little mini-light (or there's a snow pile on the light). You'll also avoid any issues with future inspections or concerns from the insurance company because you may have done something a little on the sketchy side.

  • 1
    Now we have cheap low wattage LED bulbs this is a good solution. Back in the days of incandescent bulbs, or CFLs that didn't come on if they were too cold, it wouldn't have been as good, and some way of fitting a neon lamp would have been good (they are also available, though very rare, in standard fittings)
    – Chris H
    Mar 23 at 16:11
  • "Back in the day", @ChrisH, people used incandescents because that's what they had. Mercury vapor and others gave off weird orange light and tended to buzz, so they were really only used for industrial uses (plus some took a while to warm up and weren't really suitable for regular on/off/on/off use). Plus, as a "reminder light", having one more incandescent outside is still better than leaving them all on inside...
    – FreeMan
    Mar 24 at 11:34
  • 1
    Mercury vapour wasn't orange; in the earliest forms it gave people a corpse-like pallor because of the strong green emission. Later phosphors led to the familiar fluorescent lamps (if compact and compatible with normal fittings, called "energy saving"). Sodium vapour is orange or pink and needs special lights and drivers. But all these gas discharge lamps need to warm up, and some meant for room-temperature use don't even start in the cold, as I've found in the past with my attic and my porch. But yes, in an all-incandescent setup a small one as indicator is reasonable
    – Chris H
    Mar 24 at 11:43
  • 1
    I knew it was one of those...
    – FreeMan
    Mar 24 at 11:44
  • 1
    I'm only picky because spectra are a bit close to what I do for a living, and knowing the emission features of the lab lighting has been very useful!
    – Chris H
    Mar 24 at 11:46

Anything you hard-wire into a home must be UL-Listed (or CSA or ETL). Instructions must be followed, and UL will never approve instructions for mini-lights that call for hard-wiring. As such, mini-lights invariably plug into a socket. You install a socket in the normal, proper and legal way.

If the pilot light is at the switch, you must use /3 Romex cable between socket and switch. If the pilot light is separate, then simply think of it is a room with 2 light fixtures under 1 switch control, and think of the pilot as the second light.

Follow all electrical codes. Do the work by the book. If you don't know how, the library has books on it, but don't use ignorance as an excuse to do dangerous work (and how do you know what that is unless you read up?)

What you plug into that socket is between you and your insurance company.


Use a device made for the job

Instead of faffing with trying to figure out how to mount a tiny-arse lightbulb in a standard junction box, just use something that's a premade pilot light wiring device. Legrand makes this in the form of the 2151, and Hubbell/Bryant makes an equivalent in the 48071, along with a suitable weatherproof cover, the 1795WP.

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