WOW ok let us start by NOT cutting wires.
Ok so you wanna put neon on the car.
Under it? In it? Neon tape?
Anyhoo, it doesn't really matter. What you need to do is locate the fuse box in the driver's side inside the car. You will then need to figure out what you want to do.
Do you want the neon to come on at any time?
Do you want the neon to come on only at nite and when you have the parking lights on?
To answer the first question...in other words, car is completely off, no lights on (parking or otherwise) and you have a switch to turn your neon on.......You will want to locate two things, 12 volt constant power and good ground.
Run constant power from batt to a switch (will probably be supplied with neon kit and hopefully will have a fuse). Run switch to the neon wiring and ground to a substantial piece of metal. If you can run back to the batt, run to the neg of the batt for ground.
This is the easiest way to do it. BUT if you forget that it is on or you bump the switch during the day......don't be in the least surprised if your car doesn't start. This is where you may want to find a place in the fuse panel for "switched power". What this is, is power that is only applied when you turn the switch to acc or on. This is certainly the best way to make sure that you have more control over your neon cause when the car is off, the neon is off.
To answer the second question, you will want to apply the same technique as before BUT you will be hunting in the fuse box for a fuse that has power that runs only when the parking lights are on. Remember as well that you can turn on your parking/headlights on without the car being on so again this may not be the best bet.
Remember switches need to be in place because a whole lot of our law enforcement friends don't like neon or anything like that on cars.

sheeewwwwww breathe breathe
hope that helps
L8R
Rich