You've seen the old horror films where the mad scientist is in the lab with all types of electrical equipment buzzing with arcs of electricity and sparks flying? Well, you start out by going to a neon sign company and asking for any neon sign transformers that are burned out on one side. This is a common occurrence that the transformers burn out on one side first. They usually trash them when this happens.
Now, attach heavy stiff wires to the posts bent to the shape as illustrated. The gap at the bottom has to be close enough for the spark to start. The progressive angle of the wires has to be such that the spark is inclined to travel up the distance of the wires. When it reaches the top it dissipates and a new spark starts at the bottom.
WARNING !!! This is very high voltage. NEVER adjust the wires while it is plugged in. Even unplugged, use gloves as the wires get very hot. Use extreme caution. Make sure the wires are tightened tight enough onto the posts, making sure one of the wires doesn't fall against something flammable or someone. It is safer if you construct a glass enclosure around the ladder. If you install a mirror in the back of the glass enclosure, it shows up better.
The above "How-To" is an excerpt from Tim Harkleroad's "The Complete Haunted House Book" for more information about this and other great haunted house reference books go to MoonLighting Publication's website "Haunted House Books On-Line" at www.hauntedhousebooks.com. You can e-mail Tim at moonpub@aol.com