Hey there UG, I just want to walk-through the installation of one of my LED killswitches into an old generic bass I had laying around.

The whole process too a little under 2 hours while taking my time
(minus the rewiring of the entire pickup system, I put new pups in )

Normally I want to make the hole for the killswitch inside the electronics cavity but this time I was looking to experiment and move the mounting hole further up the guitar's body.

I started by laying down some painters tape on the finish to protect it from splintering or cracking. I then drew a dot for where the center of the hole will be & tapped it a couple of times with the drill bit to make an indention.
The indention is so the bit has something to grab onto and keep it from walking around during the initial drilling.

I then proceeded to drill down at a 90 degree angle where I set my indention.
The drill speed was set high but I went on to apply very little pressure & slowly added weight once the hole started to form.

The result was a very clean cut, and it is important to use a forster style bit as opposed to a cheaper spade bit.
The spade bits tend to leave things jagged and can start to "walk" on you if you aren't super careful.

Since there is nowhere to route the wires from that location on the body, I had to route a small passageway through the electronics cavity.
I just took a large sized bit and drilled one out.

Once finished, I popped by LED killswitch into the mounting hole and routed the wires back into the electronics cavity. With that done, it was time to mount the I/O switch I was going to use to turn my LED on or off.

I wanted to mount this on the back of the guitar to make it inconspicuous, the plastic backplate was the perfect place. I started by drilled a hole with a round drill bit, a little smaller than the width of the rocker switch. Then i simply used my knife to carve it out into a rectangle where I could fit the switch snugly.

...and to clean things up a bit on this old scratched plate, I remembered I had some CF vinyl laying around, so I wrapped it.
Next I did a mock wiring of how the LED will be set-up.
The LED wires from the killswitch are Black & Red and are connected as such.
Notice I added 2 inline resistors (75ohms each), these are to tone down the power from the battery and prevent it from blowing out my LED. This is very important!

Now with my mock wiring all hooked up, I threw it all in the cavity and closed it up to test the circuit.

From here, all that is left to do it wire the remaining two wires for the Killswitch circuit itself. They're the White & Green Wires, and are actually interchangeable so you can use whichever for the ground.

At this point though, I sent off the guitar to a friend of mine to install some new pickups & potentiometers. Here's what it looked like when I got it back.

Here you can see the LED & killswitch wires are braided. Black & Red, and Green & White.

Here you can see he chose to use the green as a ground.
So the green wire will be soldered to the back of a potentiometer and then also spliced & soldered to the ground at the Input Jack( not shown), this double grounding is just for extra protection.

The White wire will simply be soldered to the Positive/Live point on the Input Jack

Another shot of the finished LED power source circuit. notice the inline resistors & contacts where shrink wrapped to prevent any short circuiting.
This killswitch I used had a total of 4 wires, 2 for the LED and 2 for the interrupter circuit.
They break down like this:

BLACK- to 9v battery negative
RED- to I/O rocker switch -> inline resistors -> 9v battery positive
GREEN- to back of a potentiometer & also to the input-jack ground
WHITE- to the input-jack positive

Green & White are reversible, and the killswitch will still function without the LED being turned on or connected.

Here's the end result.

There you have it folks- 1 LED killswitch installed on a bass guitar!

Any questions, comments or concerns? - I'll be glad to answer. Thanks for dropping by