Need some help.

My 90 bonnie has an idiot light and an oil pressure gauge. The idiot light is on, pressure gauge says everything is fine, somewhere around 50-60 lbs. I replaced the sending unit on the oil filter housing figuring it was bad but the light still stays on. Now I looked at the wiring diagram for the car and it shows that the light is un-grounded when the oil pressure opens the switch and therefore the light goes out. So in theory the if the oil pressure is high enough the light goes out or if you were to unplug the connector to the sending unit the light should go out. Now as far as I can tell the sending unit on the oil filter housing is what is driving the light so what gives? Is there another sending unit somewhere that I am not seeing? Or do I probably have a bad wire somewhere that I will have to hunt down?