Well I never really drew up a plan or anything. I simply traced a standard 3 line handle and then took the electric components, and fit them inside. As I recall I increased the size of the handle just a bit. I've attached some pictures of the layout inside. The outside pieces are 1/8” ply, the inside fill is hard balsa. Not shown is the method used to connect the flying lines. I cut slots in the fill and have bushed 4-40 bolts for the lines to connect with. The leadouts are not adjustable. The battery is turned on/off by simply plugging and unplugging the battery. The prototype had a wood trigger, since replaced with aluminum.
I use 2mm bullet connectors to connect to the lines. Although I do use the nylon coated fishing lines, I found them too heavy for small planes such as 1/2A’s. So I usually make my own. After making the lines I give them a couple of coats of clear water based varnish. That seems to be enough insulation.
I should note that I fly all electric, so all I need with this type handle in the plane is the motor esc and battery(for the motor, the control gets power at the handle)
Check this thread for more info
http://stunthanger.com/smf/index.php?topic=17457.0 . There is also a difference in Clancy’s unit and most stunt timers. If you switch planes between the two check out this thread
http://stunthanger.com/smf/index.php?topic=23922.0By the way I like what you did. It looks like you could do the same thing I am doing with less work. The black box just needs to be big enough for the battery and electronics.