Question: Finding a common wire

I just bought a house - it was built in 1966. I want to replace some light switches with timer switches that can control compact fluorescent bulbs.
I bought two different timers - a Grasslin KM2 and an Aube 1103. Both of these timers have three wires and require a common wire.
I tried to replace the first switch. It's one of three switches in a 3 gang box. Each switch is a regular one way switch.
Here's my question. What's a common wire and how do I figure out which one it is. There's a jumble of three different wires in the box - white, black and red. The switch I want to replace has two black wires to it. The switch next to it has a black a red wite to it. One of those black wires is connected to one of the black wires on the switch I want to replace.
Can I assume that this black wire is the LINE (these 2 switches get power from the same circuit - the 3rd switch is on a different circuit)? The other wires (the red on the other switch and the other black wire on the switch I'm replacing) should be the load wires, right?
So my questions are: 1. What is a common wire and how to identify it? 2. The LINE wire is the hot wire, right? 3. The load wire goes from the switch to the light, completing the circuit, right?
Thanks.
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JAG, Check with this guy - if he doesn't have your answer, nobody does! http://members.tripod.com/~masterslic/electritian.html
Best Regards, Dennis J Sunday Home Inspection Systems Www.homeinspectionsystems.com

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The common wire is the white wire. It is currently not connected to anything in the box as a standard switch needs only to be connected to the hot side. The white is passing through the box. There should be a white wire coming in attached via a wirenut to a white wire going out. Remove the wirenut and pigtail in the white (common) wire from the switch.
--
Peace,
BobJ

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