I have an outside motion sensing light which uses a nitewatch MW-12 motion detector. There is an existing Intermatic Inc. SS7 switch on the inside of the house which is very convoluted to program (there was also a V3L-2901-D9 switch hooked up to the back of the programmable switch, I'm not sure why). Some of the time I am able to get the motion detector to work and am able to turn the light on manually using the switch, but other times I can't get it to work at all. I would like to replace the existing switch with a new one that isn't so complicated and unreliable.

I took the switch out and found that there were 2 hot wires and a neutral connected to it. My guess was that the two hot wires would allow me to select whether the light should work as a motion detector, or should be on. I therefore installed a three-way switch to allow the selection of either hot wire. One position of the switch successfully turns on the light, but the other turns it off and does not make it work as a motion detector.

I'd appreciate any advice about how to get this working. Thank you!

  • Can you post a pic of the wiring in the switch box? The common, white wire, shouldn't be hooked up to the switch. And there's no need for the 3 way switch, tho it can be wired for use as a single pole switch.
    – BillWeckel
    Oct 21 '18 at 15:01

Here's what you need to know about motion sensors.

  • They already have a light sensor, and already won't turn on in daylight
  • They need time to get acclamated. Interrupting power breaks that.
  • When you connnect power to a motion sensor, it turns on for several seconds.

The motion sensor needs 24x7 power, not interrupted

A motion sensor needs power 24x7. A motion sensor needs to scan the environment repeatedly, get a sense for what "normal" looks like (and it may not be its first view), store that, and compare it to future scans.

Meanwhile the motion sensor's daylight sensor needs to calibrate itself to what day and night look like in the light location. It's not a matter of absolute lux - a light in a northern exposure in forest may see lower lux by daylight than one at night in an urban environment with street lights, traffic headlights and city glow. The sensor needs a day-night cycle or two to calibrate, and then it needs to store that data.

Your timer setup, designed to switch off plain lamps, is constantly cutting power to the motion sensor. Which does what, anyone? Anyone? Bueller?

Wipes out the motion sensor's memory. Now the motion sensor acts like a fresh install. First, it turns on regardless for a few seconds, to inform the installing electrician that the unit has good power. Then it falls back on factory settings for day/night lux until it learns (which it can't). It hasn't really had time to get clean scans of the area, it just sees this angry customer and has no idea if that guy is always there.

Sensor before switch?

The simple fix is to put the motion sensor ahead of the switch. The motion sensor has power 24x7, does its happy thing, and has no idea you have "cut the lamp connection" downstream. This only works on motion sensors with neutral wires. Oh wait. The timer needs power too.

This just doesn't work.

You have them wired in "And Logic", meaning light turns on if timer and sensor call for it. That can't work.

It is practical to wire "Or Logic", meaning the light turns on if either the motion sensor or timer calls for it. Motion sensors (with neutral) are happy being one of several things that turn a light ON. That's just not very useful.

Remembering that motion sensors already have light sensors and won't turn on in daylight.

Make up your mind

So really, this comes down to "junk the timer+switch" or "junk the motion sensor".

Honestly, motion sensors work fine if you give them an opportuntiy to settle in. Too many restless consumers don't, because they don't realize what's going on. Bypass (and eventually junk) the timer and switch.

Alternately, the timer would probably make a lot more sense if you had a plain light on it. Intermatic's steel chassis equipment is Good Stuff, if you junk it, disassemble it with respect and sell it on Craigslist.


Most motion lights need a switch so you can turn them off on the occasions when they are annoying. In addition, most can be made to stay on constantly by turning the switch off for a few seconds and then back on again. This avoids the annoyance of the light turning on and off while performing tasks in the area of the motion sensing light. Given a choice, I like to locate the switch hidden from casual use, and keep it available for my own use while working in the area.

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