Key Ignition vs. Toggle Switches

[jrevens]

Hi Grover,

I think you'd find a lot of useful information about this in the "AeroElectric Connection" by Bob Nuckolls, if you haven't already looked at that. I'll try to explain how he has suggested wiring that circuit. It's probably the simplest circuit on the airplane, so my long explanation will probably be over-kill. You can use single-conductor shielded wire for each ignition module. 16 or 18 gauge would be fine. I used 18 gauge. While shielding isn't necessary on these circuits, and even 18 gauge is bigger than it needs to be, that type/size of wire was suggested for robustness, as well as being able to cleverly use the shielding as the ground conductor. So, a pigtail is attached to the shield on each wire, and each pigtail goes to it's respective common terminal on an ignition switch (toggle, rocker or whatever). Each center conductor attaches to the N.C. terminal of it's switch. At the ignition module on the engine, the center conductors of those 2 shielded wires each goes to it's respective pin on the module connectors (the brown wire mentioned by Larry - refer to Rotax manual). The shields from your 2 wires are then connected to a grounding point ON THE ENGINE, again with pigtails. So, when a switch is "off", contact is made between the common and N.C. terminals, which connects the ignition module pin, through the center conductor to the switch and from there through the shield back to ground at the engine. When a switch is "on", that pin is disconnected from ground as the N.C. contact becomes "open". Again, you don't have to use a single conductor shielded cable - you could use a 2-conductor un-shielded cable for each module (or other combinations of conductors with or without shielding if you wanted to), but the shielded cable is generally a little tougher and more resistant to intolerable damage. It's a nice, clean way to do it, and you've also got shielding, whether it's needed or not.