mrcluster here:
Remember the rule of thumb with old estes igniters is 2amps per igniter. For simple 2 & 3 motor clusters one can get away with simply twist all leads into 2- single strands for use with a GOOD heavy gauge 12v system with a high amp/hr battery.
Always a better way is to go with a Relay Ignition System. this moves the battery from the controller side to the Launcher making a much Shorter power run from battery to igniters. Always leave a coil of lead under each igniter to allow the models first motion to lift the wires with the model allowing a bit longer for any lagging igniter to lit.
OBTW: New Estes igniters can be re-dipped in nitrocellulose lacquer made from 3- ping pong balls dissolved in 8oz of Acetone. or simply re-dipping in a pyrodex/acetone dip. I've been making my own 1ns APCP cluster igniters for decades with either alum powder or Mg metal powder. They are a bit slower then BP or pyrodex mixtures, but that work perfectly with BP motor clusters up to 12 motors.
As previously mentioned if you really want to know what is happening in those first few milliseconds after you push the button on a clustered motor model and what to see what things are absolutely necessary for "RELIABLE" cluster ignition then Please go to
www.narhams.org look in the left hand menu for the library section, go to Tech-Tips. look up and down load Tech Tip-006 "clustering BP Motors". I've recently Updated this Tip with new info and included the Range Box Relay diagram.
A simple "Range box relay" can be built for under 20 bucks from easily found parts and a simple DPDT 10amp/contact relay & socket. Diagram is printed below.
the parts list is from Radio shack but I'm sure they can be easily crossed over to any of the on-line electronic supply houses.
Hope this helps with your cluster motor flying