While the gauge face is cloudy, and that is enough to replace it if it can't be polished clear, I'd suspect the sender or wiring before the gauge. Assuming that gauge range is reasonable, it is not showing either high or low pressure. The warning light could be on because the wiring to the sender is broken, or the sender is bad. These types of gauges often use a single sender containing both the pressure transducer, and a warning transducer, with separate wires to each terminal. Check the wiring back to the warning terminal on the sender. If it is broken or a bad connection, then the light will stay on.
Mark