# How to wire 3 terminal green illuminated rocker switch?

Discussion in 'Electronic Basics' started by Kasterborus, Jan 2, 2008.

2. ### JeffMGuest

If you are going to be messing with electrical stuff,
you need to learn how to use a(n ohm) meter.

3. ### KasterborusGuest

OK so I measured the resistance and got 35 ohms between 2 pairs of
terminals, but 0 across only one pair - so would these be the
terminals to connect the 125v supply to?

This is a (hopefully educated) guess, confirmation would make me feel
better.

Dave

4. ### JeffMGuest

Confirm by throwing the switch.

5. ### KasterborusGuest

OK final question - I have a 12v DC line that I can connect to the
third (unused) terminal.

However I don't quite understand what is connected on the other side
of the lamp - the two other terminals are connected to an AC line, so
would I be able to use the 12v DC to supply the lamp?

I don't think it's possible, what do you think?

6. ### JeffMGuest

If I understand correctly, you are switching 120Vac.
So, NO. Don't do that. There is no obvious return path.

I don't see a practical path for the lamp existing.
You would have to use up 90% of the line voltage elsewhere
to get the bulb to work.
This also ASSuMEs there isn't the added complication
that the "lamp" is a LED with a low reverse breakdown voltage.

7. ### ehsjrGuest

The picture of your switch shows it is an SPST.
That means only 2 of the three terminals are connected to the
switch contact inside. One of those two terminals is also
connected to the the indicator light. The third terminal is
connected only to the indicator light.

With your ohmmeter, find the two terminals that measure 0 ohms
with the rocker in one position, and open circuit in the other
position. Those two terminals are for switching the 125 volts.
The remaining terminal (call it terminal C) connects to the
indicator bulb inside the switch. Terminal C measures 35 ohms
to one of the other terminals, regardless of the rocker switch
position. That terminal is connected to the bulb inside the switch.
The remaining terminal will measure 35 ohms to terminal C with
the rocker in one position, and it will measure open circuit
with the rocker in the opposite position.

A "schematic" of your switch looks like this:

/
o o-Bulb-o

The above "schematic" does not necessarily relate
to the physical position of the terminals on your
switch.

Ed

8. ### Rich GriseGuest

It's clearly the one against which he measured the 39 (or whatever it was)
ohms. That is, the lamp shares one terminal with one contact of the switch.

It will have to be wired in a way such that the common terminal is the
12V return, either with an isolated 12V or an isolated 115.

Apparently, in some countries, it's still legal to ground one side of the line.

And he should check if the lamp is an LED - 39 ohms sounds like a cold
incandescent.

Cheers!
Rich