You want to install Utilitec in-wall 7-day timer that has 4 wires: red, white, black and green.
You are replacing a single pole switch that controls a light or several lights.
There is not a second switch that controls same lights.
The switch has 3 wires.
Generally there are two insulated wires and a bare ground wire.
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Here's what to do:
I have tested these timers for wiring and programming.
Get started and instructions will make sense as you go.
Turn off circuit beaker to switch.
Remove old switch.
1) Timer-green-wire connects to bare ground
wire using one of the yellow wire nuts included with timer. Put two wires together so they are even at ends. Put wire nut over wire ends. Rotate wire nut clockwise between fingers until very tight.
2) Switch has 2 insulated wires. Take switch wires and connect them to
timer-red-wire using two more yellow wire nuts. Choose either one for now. You may have to reverse these two wires in a minute.
In back of electric box are white wires twisted together and covered
with wire nut. Remove the wire nut, but do not untwist the white wires. Connect timer-white to these wires. Then put original wire nut back over white wires.
4) If electric box does not have white wires described in step 3, then
connect timer-white to bare ground, along with timer-green wire.
Turn on electricity, and push ON-OFF button. If lights come on, timer
is wired correctly. If lights do not come on, then reverse timer-red
and timer-black wires from step 2.
If you need help programming 7-day Utilitec timer. Pages have bigger print:http://waterheatertimer.org/Program-wire-Utilitec-0192773.htmlhttp://waterheatertimer.org/Program-wire-Utilitec-0141224.html