Light on is overdrive(4th) cancel. If you have the box with o/d soleniod on the offside of the case, then check if it has a permenent live at the connector. O/D light on cancels this live. Check resistance of soleniod 13.8 ohms. If this is all OK remove soleniod (2 12mm headed bollts). A good flow of air should pass through the hole when powered. If hole is restricted no overdrive. If its a different box. contact specialist www.fedauto.co.uk
mags, April 2011