OK- I got it. This is how it works. With idiot lights there are four wires at the oil pressure switch- two sets of two. The two brown wires are at one tab- one is a hot coming from the C/H fuse- the other goes to the CCC for Idle Speed Control.The other tab gets two wires- a lite blue goes to the choke heater and the tan goes to the idiot light bulb. When the oil switch is open the bulb sees 12 volts from the instrument panel and lights up. It is fed by the gauges fuse and the ground is though the choke heater to the carb. When the oil switch closes the ground side of the bulb then sees 12 volts from the C/H fuse- which cancels out the circuit and the bulb goes out. The choke heater still sees 12 volts and operates. Now- WITH gauges- there is instead of the oil switch a choke heater relay. It works off the generator brown wire and when the motor is not running the "Choke Warning" bulb grounds through the choke heater. It means your key is in the ON position but the motor is not running so shut it off. When the motor runs and the generator is producing 12 volts it activates the relay and powers the choke heater. That cancels out the bulb's ground and it goes out. The oil pressure gauge uses the same tan wire as the idiot light but it is the only wire going to the sending unit. WHEW!!
