WTB Fuel Economy Indicator setup
Its a NOX device. Here is a thread that I posted asking what it was. I had it on my car. Go to page 2, that will explain it all!
http://www.forabodiesonly.com/mopar/showthread.php?t=222473
There is more to the system I believe than just that OSAC Valve. The Speedo cable also has a electrical connection on it but Im sure some how you could figure something out to trigger that light.