I would like to set this up so the first on position goes through the motion sensor and the second on position would be for just turning the led strip light on and bypass the motion sensor.
When I set this up the motion doesn’t work. Both on’s create a circuit though.
It seems that it may be due to the (-) black wire may be what the PIR uses to cut the circuit.
Does anyone have an idea how to wire this?enter image description here


3 Answers 3


On the PIR, you are shorting V- in and V- out. Are you positive the documentation says they are bridged together? If so, you can omit one wire. If not, that's half your problem.

Also you are switching the inlet of the PIR, meaning you are severing power to it. PIRs often need to "get a sense of the lay of the land" which they then store and use as a reference for "unoccupied". If they also monitor day/night, it helps them to go through a couple of 24hr cycles to learn what your location's highs and lows are. These units do not have expensive NVRAM: If you sever power, it's like a factory reset.

So supply + and - to the PIR inputs at all times. Put the PIR output on one switch leg, constant power on the other, and to the LED in the middle. Whether you switch + or - should depend on what the PIR switches... check its docs. If you are not sure, get a DPDT and switch both.

enter image description here

If you can confirm that one of those wires is bridged inside the PIR, you can nut them all together, eliminate one of them to the PIR (redundant) and use a single-pole (SPDT) switch.

  • I don't think there would be a need to switch the ground if the pir needs to be powered all the time just switch its hot output using the existing switch with the input to the pir hot all the time.
    – Ed Beal
    Feb 9, 2018 at 14:22
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    @EdBeal i see your point in that DC electronics often uses V- for GND aka common, e.g. Computers, cars. However that is the very first thing OP tried, and it didn't work, so we can cross it off the list. He may have befallen that same assumption, which is a mistake especially in the LED strip world. I would not make any assumptions about common unless each data sheet tells me to. Here, the + may be common. Feb 9, 2018 at 19:39
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    In LED strips and controls, I see a lot of "+ is common" . That is for good reason. May 26, 2018 at 18:41
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    @EdBeal The problem is we don't know which side is switched in the PIR, hence the need for a DPDT switch. Can you honestly say you know whether the PIR switches - or +? Or are you just assuming after many years in electronics where most things are? Look at the PIR, V+IN and V+OUT right next to each other. Why do that? May 27, 2018 at 15:05
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    @GlennWillen yes, also commonly seen in automotive design, open-collector TTL, etc. Easier to sink than source. Nov 1, 2018 at 0:09

I think you will need to jumper the blacks, it should not be a problem that is now your ground or common. The led will fire up when in that position and the motion sensor will light the led in that position.


If you take all wires out and use a Multimeter Are the V+'s connected or the V-'s connected?

Whichever one is not connected you can use a SPST switch to bridge that side. this will eliminate a bunch of wiring and allow you to have the minimal circuit that works for your desired application.

My guess looking at the device is that the V+'s are connected, since they are next to each other on the circuit board and the V-'s are switched.

if neither of them are connected then they are using a DPDT relay, I would then choose one, V+ or V- to short across, and then use the single SPST switch to bridge the other side.

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