I have a phone outlet in my house for a second line. I only subscribe
to one line and I would rather have this outlet for an extension on
that line. How do I modify the wiring to accomplish this?

Assuming that everything is wired properly through out your house, and
nobody has made any unusual repairs along the way, it is relatively
easy to switch an individual jack from line 2 to line 1.

I sheepishly admit that I've rewired my phone jacks plenty of times
without doing this, but for safety reasons you should always
disconnect the power at the network interface device before you do any
work on your wiring. Quite a bit of power goes through the line when
the phone rings, and you don't want to get shocked. You can usually
find the network interface device in your basement, if you have one,
or on an outside wall of your house. It is usually a small, neutral
colored plastic box. (The page I reference below says the box is gray,
but mine is black and I happen to know my mother's is light tan.)

Once you're ready to begin, start by unscrewing the jack from the
wall. Connected to the jack should be a four-strand wire. The strands
should be colored green, red, black and yellow. The red and green
wires normally connect line 1, and the black and yellow pair connect
line 2. To switch the jack from line 2 to line 1, disconnect the black
and yellow pair (most jacks just hold the wires down with screws) and
then connect the red and green pair in their place.  Plug in a phone
and listen for a dial tone to make sure you have a good connection,
and once you're sure everything is snug, screw the jack back into the
wall and you're done. It's very easy.

If you need more help, this page has pictures of what the wiring looks
like as well as further instructions on how to handle some of the
alternate configurations:

    Doing your own telephone wiring
    http://www.ling.upenn.edu/~kurisuto/phone_wiring.html

I hope this helps, and if you need any further clarification, do not
hesitate to ask.

-Spot


Doing your own telephone wiring
http://www.ling.upenn.edu/~kurisuto/phone_wiring.html

The Basics of Telephone Wiring
http://telecom.hellodirect.com/docs/Tutorials/TelWiringBasics.1.040401.asp

Bang-up job. I spent twenty dollars Wednesday buying a new cordless
phone, and five dollars today learning I don't need one! Net savings:
$15. Thanks, spot! Now, where's that receipt...

Make sure that you do not exceed the maximum REN(Ringer Equivalence
Number) by
connecting lot of phones to the new extension line.  Normally the
electronic phones
have an REN of 0.2, where a manual phone(where the ringer is powered
by the line itself)
consumes around 0.8-1REN.  Just add up the REN's of all the phones
connected to
get the total REN.  A REN of around 4-5 should not create a problem,
but more than
that could create malfunctioning of the connected phones(some may not
ring), apart
from the extreme case of your local carrier disconnecting your line
temporarily for
overloading their exchange power supply.

Been there Done that!.

Regards
ldavinci-ga