I thought I'd try to be all helpful around the house and replace the PIR light switch in my dad's room with a simpler timer switch. After flipping the breaker, I pulled out the PIR and found that there were four wires. I was only expecting black, white, and green, but it had a red wire like a 3-way switch. Except that this switch isn't supposed to be 3-way and there isn't any other switch in the house that controls this light.

I looked up the manual for another manufacturer's PIR light switch, and for 2-way operation it says to cap off the red wire. I'm wondering if I should do just that -- cap off the red wire in the wall, and just connect the other three wires as I normally would. Can anyone offer me their advice?

2 Answers 2


Switches normally just "make or break" the hot lead. Neutral conductors should never be connected to switches except for PIR wall switches and many wall timers. They need to have a neutral connector.

So you should have:

1) constant live hot wire (normally black in USA, but you never know without testing)

2) switched hot wire that delivers switched power to the load (I use red for that, never know...)

3) ground wire (green or bare)

4) Neutral wire (normally white...)

Carefully test, you should be able to identify.


All AC switches in home wiring have at least two hot leads. These may be in the form of terminals on the switch (either screw, push-in connections, or both), or wires permanently attached to the switch.

The most common switches are:

Basic switch (SPST) [old]

The simplist switch, in the pre-ground days had just two terminals

  1. hot in
  2. hot out

The wires to this switch should be black (most often) or red, or a combination of these. White wires can be used if they are marked as hot with tape or a marker.

This switch is also called single pole, single throw (SPST), because there is one line (pole) being switched and only one of the switch positions (throws) makes a live connection.

Basic switch (SPST) [new]

The simplist modern switch has three terminals

  1. hot in
  2. hot out
  3. ground

Same as old version but a green or bare wire goes to the ground terminal.

Basic 3-way switch

This switch is used when there are two switches used to control a device. It has four terminals

  1. hot (common)
  2. traveler 1
  3. traveler 2
  4. ground

The hot (common) of one of the 3-way switches is connected to the live load. The common on the other switch is connected to the device to be switched. The travelers of one switch are connected to the traveler terminals of the matching 3-way switch.

Basic four-way switch

This switch is used when there are more than two switches used to control a device. It has five terminals

  1. traveler 1 in
  2. traveler 2 in
  3. traveler 1 out
  4. traveler 2 out
  5. ground

This switch sits between two three way switches. Both travelers from one 3-way switch go to one side of the 4-way, and both travelers from the other 3-way go to the other side. The 4-way is never directly connected to the mains or to the switched device. Multiple 4-ways can be used if you want more than three switches on a line, but they are all between the original pair of 3-way switches.

Active Switches

These can be any of the switches listed above. These are characterized by having some feature other than basic switching, such as

  • illumination
  • dimming
  • timing
  • motion sensing

These have the same terminals as the basic switches, but usually add a neutral terminal (or white wire) to complete a circuit within the switch itself. A few active switches are designed to operate without a neutral. Check manufacturers' instructions.

There are numerous other, more complex switchtypes, including double pole, double throw, programmable, master, slave, etc. with various wiring requirements.


Your switch is a SPST switch, but it is active because of the PIR or timer functionality. Connect the black wire to the hot line in, the red wire to the device being switched, the white wire to the neutral in and the green wire to the ground in.

  • Thank you for the great amount of detail. I have a Lutron timer switch (westsidewholesale.com/…) and it only accepts two wires. Am I to assume that I just use black and red, then? I guess the timer functionality is powered from the mains?
    – Dave
    Aug 6, 2014 at 23:02
  • From the Lutron site, it looks like the switch does not require a neutral. If that is the case, you would just use the black and red. Note that the switch you link to is a dimmer switch, not a timer.
    – bib
    Aug 7, 2014 at 14:41
  • Oops, I think it's this one, my mistake: westsidewholesale.com/lutron-ma-t51-wh.html. I'm hoping to get that thing installed today!
    – Dave
    Aug 13, 2014 at 12:58

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