I'm building a Multi-Pad-Launch-Controller originally designed by John Hruby and posted to the NAR.org site in May 2014 (parts and design being updated somewhat). I've attached my wiring diagrams for the launch controller and relay box. I'm still fiddling with the design components (I need low input voltage relays vs. standard 12v relays and a DB9 cable with a bigger gauge wire to minimize voltage drop to the relays) but have it working. The intent is to be able to launch up to four rockets concurrently. I'm using a 100 foot DB9 cable so I can comply with NAR safety code for HIJ engine flights (my launch pad converts from a four rod pad to a single rail pad using a jawstand). Here's my issue. The voltage drop over 100 feet is notable, but I can fix that with the two adjustments noted above. In testing, when I have one pad active, the voltage for relay one at the relay box is 10+ volts. All good. HOWEVER, when I activate pads 2, 3 and 4, the voltage across the active pads drops with each pad activated, roughly 7.5 volts with two pads, 6+ volts with three pads and 5+ volts with 4 pads. Voltage on these circuits at the controller end is nominal for all pads. Each circuit is independent, so why is the voltage dropping as I activate pads? I'm driving the controller box with a SLA 12 amp hour battery. I'm not an electrician, but I'm not a newby either and I'm stumped. Does anyone know why I am seeing this characteristic? Thanks in advance.