If they had caps in TRON, this is what I think they might look like.
Step 1: Materials
EL Wire colour of your choice (around 2m)
AA battery Inverter
Thin clear fishing wire
Super Glue (Not shown)
AA Batteries (Rechargeables will work)
Snips (Not shown)
Step 2: Planning
Now this is 'Ible is for a cap but it can be applied to most head wear.
Figure out which parts of the cap you're going to light up and where you're going to route any wires extra EL wire etc...
For me my original plan was to go along up, back down the way I came and along all the way round. That was until I found that for this thickness wire it would only bend about 4/6 of the way on itself, so I came up with the layout you see above.
I hid the run from the back to the front to light up the rim on the inside of the seam and at the back put a bit of heat shrink on to make it symmetrical.
Step 3: Sewing
Using the needle and fishing line, sew the EL wire to the cap in your design. I sewn the EL wire about every 3-4cm or at every corner, and then 4 times in total on the verticals. Then using the super glue, glue your knots (if sewing isn't your strong point like me) just to make sure they don't undo in that moment you really don't need them to... say walking around town at an event for example.
Once you've got it all sewn up, pop in some batteries into that inverter and see how it looks!
Once you're happy with how everything is positioned, we need to sort out the battery pack/inverter.
Step 4: Battery Pack/Inverter
My EL wire came with a battery pack and inverter in one. It even has three modes; constant on, flashing fast (look out epileptics) and flashing slow.
Anyway, I used rechargeable batteries. The people that make the inverter said to use alkaline batteries but thankfully rechargeables work too. Even though the rechargeables input only 2.4V instead of 3v the alkalines would input.
The batteries in the picture have a capacity of 2000mAh, I've tested them with the EL wire on constant with fully charged batteries and they ran for 8+ hours. The batteries rattled a little in the holder so I cut a piece of foam to put into there with them and that sorted that out.
I also cut up some more foam to put on the sewn knots in the parts of the cap that rest against my forehead to stop them scratching.
Step 5: Finishing Up
I found two places to be acceptable, on the back of the cap on the adjustable Velcro and the other on the back of my T-shirt on the neck.
On the cap itself made the whole thing very mobile and easy to remove, change modes etc... but left the inverter annoyingly close to my ears with the high pitch whine it put out.
The back of by T-shirt under a hoody was much better and didn't hinder movement although it can be tricky to reach the button on the inverter.
Thanks for reading and I hope you found this 'ible helpful, it's in the "Make It Glow" contest so if you think it worthy do vote!