Prowling around on EBay, I noticed this .. which provides a variable output voltage from 0 to 5 volts rather than a relay closure. Voltage is increased or decreased with a pair of "up/down" buttons.
The published "power required specs" are weird though .. says 36 volts .. which logic would tell me is a max, with it most likely running on 12 volts.
http://cgi.ebay.com/RF-Wireless-Dynamic-...1742.m153.l1262
