Install timer in wall

[stanepstein]

Ok, here goes. A switch in my garage controls the light mounted outside the entry door. I bought an inwall timer that has red, blue and black wires. The instructions say connect one wire from the house to the black wire and the other house wire to the blue wire. The current circuit is not a three way. The power to this circuit also controls the family room light and outlets. The circuit in the wall has 3 white wires wire nutted together and 3 black wires going to the switch, One blk wire is on a screw terminal, another goes into a slot near that screw terminal. The 3rd blk wire goes into a slot at the top of the switch.
Since I had 3 blk wires I connected each of them to a wire from the timer, including the red wire. The result is that there is no power to anything in the family room but the outside light can be switched on and off by the timer.
I took everything apart and put it back like it was and now everything is back to normal. I need to know how to wire this timer. What am I to do with the 3 white wires nutted together and why is this wired like this?

Thanks in advance!

[mdshunk]

Manufacturer and model of the timer would be helpful so that we can look up the instruction sheet.

[Homer]

What am I to do with the 3 white wires nutted together and why is this wired like this?I'm sure that you have three 2-wire cables in that box.

1) Power feed in.

2) Switched power to light fixture.

3) Unswitched power out to next device (switch or receptacle).

All three white neutral wires will be wirenutted together.

This is a very typical setup. Once you provide some info on the timer we can tell you how to wire it.

Homer

[Roger]

I'm reasonably sure you have a timer that can be used with three way switches or a single pole switch. It also sounds like an electronic timer that doesnt require a neutral. As Marc said if you provide us with the maker we can answer more positively. I'll provide you with one way to wire the timer. It would be adviseable that you wait till Marc can reply after you provide the information he asked for.

I also agree with Homers wiring logic.

Your description indicates a single pole switch. You would wire the timer as follows. Cap off the red wire it is not used for a single pole switch. On the existing switch remove the black wire on the screw and the black wire in the hole adjacent to it. Take those two wires and the black wire of the timer and put all three of them together in a wire nut. Now take the remaining black wire on the switch and connect it to the blue wire in a wirenut, Leave the whites as they are and keep the grounds together and ground them to the timer if the timer has a grounding termination point. You may or may not have ground wires you dont mention any.