user4446: I understand that el wire and paper needs a special power source known as an inverter to light it up.
If I wanted to control it from an arduino, what point would I connect the arduino to the light or inverter?

user186: upstream slow blinking
The simplest approach:
Use a relay to turn the lights on and off. Control that relay with an Arduino.
("How to turn a relay on and off with an Arduino?" is a separate question).
Cut either one of the wires feeding power into the EL inverter ("upstream of the inverter"),
and connect the 2 cut ends of the (formerly) one wire to the contacts of the relay.
power source ---- (relay contacts) ---- EL inverter ---- (EL wire)
           +--------------------------------+    +---------+

downstream slow blinking
Alternative approach:
Use at least 2 pieces of EL wire.
Wire one always-on;
use a relay to connect or disconnect the other wire ("downstream of the inverter"). (The relay and controlled wire can be either directly connected to the inverter, or end-to-end connected to the always-on wire -- it doesn't matter for this application).
                                   always on
power source ---- EL inverter ---- (EL wire) ---- (relay contacts) ---- (EL wire)
           +----------+    +---------+   +-------------------------------+

Control that relay to control the EL wire with an Arduino, same as before.
dimming and PWM
Many low-cost relays are rated for only about 10,000 operations, so if you use them to blink for a long or short part of each second, they're only guaranteed to last for about 3 hours.
If you want to blink faster than that (and most people dim EL lights by blinking them much faster than that), you'll have to use something other than a relay.
Also, most people seem to want to do the switching "downstream" of the inverter, so they can "share" a single EL inverter and use it to power lots of independently controlled pieces of EL wire.
Perhaps the simplest approach is to use an off-the-shelf zero-crossing solid-state relay (SSR).
("How to wire a SSR to an Arduino?" is a separate question).
power source ---- EL inverter
          +-----------+   | |
                          +----- EL wire (always on)
                          | +-----+
                          | |
                          +----(SSR)-- EL wire
                          | +-----------+
                          | |
                          +----(SSR)-- EL wire
                          | +-----------+
                          | |
                          +----(SSR)-- EL wire
                          | +-----------+
                          | |
                          +----(SSR)-- EL wire
                          | +-----------+
                          | |
                          ... etc.

Because most SSRs are overkill for this application -- most of them have heatsinks bonded to high-power triacs designed to handle far more current than we need to light up a EL wire --
some people save a few dollars by assembling their own SSRs out of zero-crossing optocouplers, triacs, etc.
(A lower-cost, low-power triac is more than adequate for controlling EL wire, even without a heatsink).
The SparkFun EL Escudo Dos Arduino shield for controlling electroluminescent wire(c)(d);
Diana's SparkFun EL Sequencer(e)(f)(g);
the seeedstudio EL Shield(h)(i)(j)(k);
Tully Gehan's Cool Neon Arduino Shield(m)
etc.
uses such zero-crossing optocouplers, triacs, etc.
(requires a separate EL inverter).
According to some people on the Arduino forums talking about EL wire(n)(p),
some people save a few pennies by using normal optocouplers rather than zero-crossing optocouplers. Non-zero-crossing optocouplers seem to work fine for short pieces of EL wire but seems to destroy the triacs (failing "always on") with a few dozen feet of EL wire.
Some people save a few more pennies by skipping the optocoupler,
wiring the Arduino directly to the control gate of the triac, and the VCC pin of the Arduino directly to the MT1 pin of the triac.
(q) (r) (s) (t)
If there were some way to only turn the triac on near the zero-crossing, this could work great; but without zero-crossing control, this has the same problems as the above normal non-zero-crossing optocouplers.
always-on
The "extra" always-on bit of EL wire is because some people say
"never run the inverter without at least 1 foot of EL attached"(a) because running some EL inverters with no load "can damage the inverter"(b).

4446: <p>I understand that el wire and paper needs a special power source known as an inverter to light it up.</p>

<p>If I wanted to control it from an arduino, what point would I connect the arduino to the light or inverter?</p>
 186: <h2>upstream slow blinking</h2>

<p>The simplest approach:
Use a relay to turn the lights on and off. Control that relay with an Arduino.
("How to turn a relay on and off with an Arduino?" is a separate question).</p>

<p>Cut either one of the wires feeding power into the EL inverter ("upstream of the inverter"),
and connect the 2 cut ends of the (formerly) one wire to the contacts of the relay.</p>

<pre><code>power source ---- (relay contacts) ---- EL inverter ---- (EL wire)
           +--------------------------------+    +---------+
</code></pre>

<h2>downstream slow blinking</h2>

<p>Alternative approach:
Use at least 2 pieces of EL wire.
Wire one always-on;
use a relay to connect or disconnect the other wire ("downstream of the inverter"). (The relay and controlled wire can be either directly connected to the inverter, or end-to-end connected to the always-on wire -- it doesn't matter for this application).</p>

<pre><code>                                   always on
power source ---- EL inverter ---- (EL wire) ---- (relay contacts) ---- (EL wire)
           +----------+    +---------+   +-------------------------------+
</code></pre>

<p>Control that relay to <a href="http://www.instructables.com/id/Control-EL-Wire-with-an-Arduino/" rel="nofollow noreferrer">control the EL wire with an Arduino</a>, same as before.</p>

<h2>dimming and PWM</h2>

<p>Many low-cost relays are rated for only about 10,000 operations, so if you use them to blink for a long or short part of each second, they're only guaranteed to last for about 3 hours.
If you want to blink faster than that (and most people dim EL lights by blinking them <em>much</em> faster than that), you'll have to use something other than a relay.</p>

<p>Also, most people seem to want to do the switching "downstream" of the inverter, so they can "share" a single EL inverter and use it to power lots of independently controlled pieces of EL wire.</p>

<p>Perhaps the simplest approach is to use an off-the-shelf zero-crossing solid-state relay (SSR).
(<a href="https://arduino.stackexchange.com/questions/4545/how-do-you-wire-a-ssr-relay-to-a-arduino-nano">"How to wire a SSR to an Arduino?"</a> is a separate question).</p>

<pre><code>power source ---- EL inverter
          +-----------+   | |
                          +----- EL wire (always on)
                          | +-----+
                          | |
                          +----(SSR)-- EL wire
                          | +-----------+
                          | |
                          +----(SSR)-- EL wire
                          | +-----------+
                          | |
                          +----(SSR)-- EL wire
                          | +-----------+
                          | |
                          +----(SSR)-- EL wire
                          | +-----------+
                          | |
                          ... etc.
</code></pre>

<p>Because most SSRs are overkill for this application -- most of them have heatsinks bonded to high-power triacs designed to handle far more current than we need to light up a EL wire --
some people save a few dollars by assembling their own SSRs out of zero-crossing optocouplers, triacs, etc.
(A lower-cost, low-power triac is more than adequate for controlling EL wire, even without a heatsink).</p>

<p>The SparkFun EL Escudo Dos Arduino shield for controlling electroluminescent wire<a href="https://www.sparkfun.com/products/10878" rel="nofollow noreferrer">(c)</a><a href="http://rylaangimby.com/holographic-fortune-teller-arduino-el-wire-unity/" rel="nofollow noreferrer">(d)</a>;
Diana's SparkFun EL Sequencer<a href="https://www.sparkfun.com/products/11323" rel="nofollow noreferrer">(e)</a><a href="http://makezine.com/2010/04/27/programming-el-wire-fashion/" rel="nofollow noreferrer">(f)</a><a href="http://www.kobakant.at/DIY/?p=2992" rel="nofollow noreferrer">(g)</a>;
the seeedstudio EL Shield<a href="http://www.seeedstudio.com/depot/EL-Shield-p-1287.html" rel="nofollow noreferrer">(h)</a><a href="http://www.seeedstudio.com/wiki/EL_Shield" rel="nofollow noreferrer">(i)</a><a href="http://www.bajdi.com/trying-out-the-new-seeedstudio-el-shield/" rel="nofollow noreferrer">(j)</a><a href="http://www.robotshop.com/en/el-shield-arduino.html" rel="nofollow noreferrer">(k)</a>;
Tully Gehan's Cool Neon Arduino Shield<a href="http://shopping.netsuite.com/s.nl/c.ACCT88394/it.A/id.1071/.f?sc=2&amp;category=1678" rel="nofollow noreferrer">(m)</a>
etc.
uses such zero-crossing optocouplers, triacs, etc.
(requires a separate EL inverter).</p>

<p>According to some people on the Arduino forums talking about EL wire<a href="http://forum.arduino.cc/index.php?topic=50534.0" rel="nofollow noreferrer">(n)</a><a href="http://dorkbotpdx.org/blog/paul/sparkfun_el_sequencer_trouble" rel="nofollow noreferrer">(p)</a>,
some people save a few pennies by using normal optocouplers rather than zero-crossing optocouplers. Non-zero-crossing optocouplers seem to work fine for short pieces of EL wire but seems to destroy the triacs (failing "always on") with a few dozen feet of EL wire.</p>

<p>Some people save a few more pennies by skipping the optocoupler,
wiring the Arduino directly to the control gate of the triac, and the VCC pin of the Arduino directly to the MT1 pin of the triac.
<a href="https://kavasmlikon.wordpress.com/2011/11/21/how-to-make-el-wire-blink/" rel="nofollow noreferrer">(q)</a> <a href="https://electronics.stackexchange.com/questions/25295/arduino-triggering-a-triac-for-el-wire-no-optoisolator">(r)</a> <a href="http://celestialaudio.com/catchall/" rel="nofollow noreferrer">(s)</a> <a href="http://www.opencircuits.com/Russ_Hensel&#39;s_EL_Wire_Project" rel="nofollow noreferrer">(t)</a>
If there were some way to only turn the triac on near the zero-crossing, this could work great; but without zero-crossing control, this has the same problems as the above normal non-zero-crossing optocouplers.</p>

<h2>always-on</h2>

<p>The "extra" always-on bit of EL wire is because some people say
"never run the inverter without at least 1 foot of EL attached"<a href="https://learn.adafruit.com/el-wire" rel="nofollow noreferrer">(a)</a> because running some EL inverters with no load "can damage the inverter"<a href="https://learn.adafruit.com/el-wire/using-el-wire" rel="nofollow noreferrer">(b)</a>.</p>
