Join Date: Mar 2002
Location: Austin, TX, USA
Sounds like one of the first things you should do is get a schematic and see how many senders are on the vehicle. It is very likely that there are two separate ones. One for the guage and one for the ECM. It is likely that the ECM is what is illuminating the light, but that isn't a conclusive diagnosis without knowing exactly how many sensors are on the engine.
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI