ORIGINAL: evdreamer
Do you know what kind of voltages the signal pin has when you turn the 5th channel knob? If it went under 2.5V and above it couldn't you use a transistor as a switch? Would hooking the signal pin to the base of a transistor then have the collector and emmiter inline with the positive pin and light work? I never checked out what was going on with the signal pin before so maybe that idea wouldn't work also. But I didn't know if lizrd56 wanted them to blink or just turn on or off.
The signal pins works completely differently from what you're thinking. It's not varying a voltage level, it's sending a repeating pulse. What changes is the width of the pulse. Do a google search on RC radios and you can find all kinds of info.
You can make a circuit to switch the lights on and off, but it's not quite as straight forward as you think since you need to sense the pulse width and use that to switch the transistor on and off. I've done it with a dual D flip-flop IC, RC filter and BJT. Took me a long time to find the circuit on line (you'd think it would be more common) and I'm not sure if I bookmarked it, but I can explain it to you if you're interested, it's pretty simple once you get it.