Update: Working link for the trailer is here: http://www.youtube.com/watch?v=4YvNVqf2at0
Step 1: Supplies
First thing, gather your materials:
Some sort of plank of wood. The one I used here isn't ideal because it is thin enough for the nails to come through the other side.
Smaller chunk of wood for mounting pickup
Step 2: Setting Up the String(s)
Decide where you want your string to be positioned. Stick a nail in each end of the board in that position.
Place the bottle up against one of the nails, and mark where the other side of the bottle is. Put another nail in this spot (this will keep the bottle in place).
Remove the bottle, and fasten the string around the nails on either end of the board. Make it tight enough that it's quite hard to slide the bottle back in.
Put the bottle in place. Now you've got the acoustic version of the cheapest guitar ever made.
Step 3: Wiring the Pickup
When making this guitar, I wired the pickup first before fixing the pickup in place so I could tell where to put it in order to get a good signal. The pickup I used is a DiMarzio Super Distortion humbucker, which has five wires for splitting the coils. Since I wanted to use both coils, I doubled up the wires from each coil. If you have a similar pickup, then refer to the pictures for instructions. Otherwise, I can't help you as I really know don't know much about wiring. Please excuse my poor instructions in this step. Here's what I did:
Black and braided wire - attached to tab on output jack connecting to shaft of the patch cord.
White wire - attached to tab connecting to patch cord tip.
Green and red wire - electrical taped over then taped out of the way.
For the moment, I have not soldered the wires in place. If you just want to wrap the wires around their respective connections, it works fine but is not very permanent.
Step 4: Placing the Pickup
Next, take your pickup and output jack, and plug it in to your amp. Line up your pickup to your guitar, and find a good place under the string where you get a nice strong signal. Mark it on the board.
Next, take your smaller chunk of wood, and nail it in place. This board should be thick enough to raise the pickup to the desired height. Screw or nail the pickup to the board.
Step 5: Play It
Now you're finished. Get out your slide and play it. If you want to tune it, hammer in one of the end nails a bit until you've got the right pitch. Also, I've found that the nail holding the bottle in place can be used as a whammy bar. Wicked, huh?
The next thing you could do would be add another string or two and put them in drop-d tuning or something like that. Good luck.