On my '81 with factory Rochester Q-Jet carb, I have juice to the wire that goes on the electric choke according to my test light but when I plug it onto the tab on the carb for the electric choke, the hook up my test light, it doesn't light the test light anymore.  Why?  Any advice would be appreciated thanks, George

With the wire disconnected, there is voltage because there is nothing loading the circuit(not going to ground/open circuit).
With the choke plugged in, the voltage is going to ground, thru the choke coil, making the circuit complete, and "using up" the available voltage.
That is how DC electrical circuits work. Positive(+) voltage must find it's way to ground(-), in order to have a complete circuit.
So...what you are seeing is an electrical circuit that is working properly.

George, you're better to test with a multi meter - this will allow you to test both the voltage and the current flow.

1) Multimeter switched to 12 Volt range (or higher). Black ( - ) probe connected to a good earth, red ( + ) probe connected to choke wire tab with wire connected, key on, you should see some voltage though as Adam says may well have dropped to something less than 12V due to circuit load of choke coil.

2) Meter switched to 10 Amp scale, disconnect choke wire from tab. Red (+) probe to wire, Black (-) probe to tab. Key on, and you should see a healthy current flow indicated by the meter if the choke coil circuit is good. If the choke coil is bad you will see no current flow.

Make sure you turn the key off first each time you change the probes and the meter settings.

If it helps, think of it like water in a hose. Voltage is the electrical equivalent of water pressure, wanting to move the water through the hose, but if the tap is off there is no water flow, but the pressure (voltage) is still there at the tap. When you turn the tap on ( equates to turning the electrical switch on) the water can now flow - which equates to electrical current flowing in the wires, as a result of the voltage "pressure" pushing it.

The only fundamental difference with this analogy is that electricity MUST have a "hose" (wire) to flow through, otherwise it just stops (as is the case with a broken wire.) Water on the other hand will happily flow where ever it likes whether it has a hose or not !!!

Cheers, Chris

Much thanks guys.  Nice analogy too malo682008-04-13 17:58:27