The "extra" input would normally be plugged into a battery. That's the 4th connection I was talking about? It's no longer necessary if you're getting power from the "control" connection, the one that's pluggged into the receiver that's used to turn the switch on and off?

The reason it's markd <20v is because it's able to switch devices other than ign. modules? Stuff that may be set up to run on higher voltage.

The newer ign. modules are rated for up to 8.4v. They would not need a voltage limiting circuit as part of a BEC. It's why VV is selling them both ways. -Al