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Old 05-28-2019, 05:24 PM
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Zenith carb wiring question....

A friend of mine is rebuilding a 1965 W111 with a six cylinder and the dual Zeniths. He just about has it all together. But he did have a wiring question.

He showed me a wire from the firewall and asked where is this attached? So I looped it around and showed him an electrical connection on the front and bottom of the front carb. Then he could easily see where the wires (Which are two wires in a sheath) connected, which is to two screws, but he didn't know which wire went on top and which one went on the bottom.

One wire is brown, so that has to be the ground, and one is sort of a faded red. I have searched by manuals and cannot find the answer for him. I didn't take this apart so I don't have any notes or photos.

So could someone look at their wiring and tell me if the brown wire is on the top of the connection or the bottom?
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Old 05-28-2019, 05:43 PM
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This device sounds like an idle circuit cut off / high idle solenoid. Are there any markings on the device terminals?

Run an ohm meter across the terminals and then terminal to ground. If neither terminal conducts to ground, I'd expect wire location not to matter. I also doubt that they would have put a clamping diode in the device without some sort of markings.
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Old 05-28-2019, 10:08 PM
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There are at least two sets of wires to worry about, depending on the year of the carb and the car.

Early carbs just have a wire to the warm up device for the secondaries. That is switched on with the ignition and says on always.

Later carbs have a fuel cut-off solenoid that is basically wired the same way. It's an emissions thing, not a fire safety, so it doesn't stop fuel flow to the bowl, only the idle circuit gets cut off.

Both should be managed through wiring back to fuse panel, but they are set up as separate paths from the fuse panel if you are following the factory wiring pattern. There's a service bulletin someplace that mentions the idle solenoid cut-off when a newer carb is retrofitted to an older car. It tells you to run that wire to fuse 4. I recall it also suggesting its own fuse, in case the solenoid wiring shorts to ground.

-CTH
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Old 05-29-2019, 12:07 AM
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It could be a throttle position switch that unlocks the automatic transmission when slowing to a stop so it doesn't clunk.
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Old 05-29-2019, 07:17 PM
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Quote:
Originally Posted by 97 SL320 View Post
This device sounds like an idle circuit cut off / high idle solenoid. Are there any markings on the device terminals?

Run an ohm meter across the terminals and then terminal to ground. If neither terminal conducts to ground, I'd expect wire location not to matter. I also doubt that they would have put a clamping diode in the device without some sort of markings.
An idle circuit cut off is what it looked like to me as well. But there are no markings on the device and it is really small. My elderly eyes have a lot of trouble focusing on it but I could tell it is there. This would take such a small screwdriver that a large jewelers screwdriver would be just about right.

I didn't even think about looking for the ground using a meter. I will pass that on to him tonight.

Thanks.
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