I replaced the sensor on the column with a simple voltage divider circuit. I used a 16k resistor and a 3.3k resistor. The 16k connected to sensor return (ground) the orange/black wire, the 3.3k connected to +5 vdc the grey wire. Then I connected the light blue wire to the connection of the two...
My 99 classic was having similar issues. I found that I had a bad positive battery cable. The truck would start and run fine but sitting overnight there was enough voltage drop because of the cable my ECU would set the monitors to not ready.