Well, I have an 86 chevy truck.. It has a quadrajet with electric choke. The wire coming off of the oil pressure switch is supposed to run the choke. When the motor is running, my meter reads 12 volts. As soon as I plug the wire onto the carburetor, my meter reads zero volts, and the juice never gets to the choke to heat it up. I have ran a switched hot wire from in my cab, from the battery, to the choke. It reads 12 volts, and continues to read 12 volts when I hook it to the choke, and the choke heats up and opens. I cannot figure out why the voltage drops from 12 to 0 when I hook up the correct wire. I have even replaced the oil pressure switch, hoping that would work, and it didnt. Not sure what to do next.

Any suggestions,,??

robert

You should have a pink and white wire hooked to the oil pressure switch. This feeds the choke coil when the engine starts through the light blue wire on the oil pressure switch. There should be a dark blue wire hooked there also and it connects with the oil sender through a tan wire.
You may be reading the 12 volts through the choke light and the oil pressure sender with the engine off and when you start the engine and build oil pressure the resistance through the sender to ground builds up and causes a voltage drop when you hook up the choke wire . I hope this makes sense to you. Check the pink/white wire first and see if it's on the oil pressure switch.
You can hook a keyed 1`2 volt source to the choke and it will work. "That's how the guys with the older trucks do it when they install electric chokes.
Actually that is what the pink/white wire is except it goes through the oil pressure switch and becomes a light blue wire to the choke coil. Good luck V.V.

Sounds like a resistance problem. It reads 12V but you have a weak connection and it will not take any amperage. I would clean all connections on that circuit and see what you get. John