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Discussion Starter · #1 · (Edited by Moderator)
just curious ive never had a choke light before, what causes it to go on and off and why does the driver need to know what the choke is doing?
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The light is just letting you know if the choke is engaged or not. On these trucks / rochesters the choke is electric and the switch that controls the choke is powered key on ignition.

The choke is just a way of helping the engine cold start. It "chokes" or limits airflow through the carb. A blade closes cutting off airflow - creating a richer condition to help the motor start up. The light is neat because if you know the choke is staying engaged or not engaging at all it can help you diagnose rough start or rough idle conditions.

I'm ls swapping mine and figure I'll use the choke light as my check engine light.
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Discussion Starter · #4 ·
how does the light know when to go off? and what book is that diagram in?
 

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how does the light know when to go off?
The black thing on the side of the carb is the electric choke controller - it's a thermostat. A switch that's thermostatically controlled. When it's working right, it engages your choke and closes the primaries until it gets to an operating temp and then disengages - which should kill the light at the same time.
 

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Discussion Starter · #10 ·
you said if the ignition switch is on then the bimetal strip is getting power which heats it up and opens the choke. The light would always be on then. im asking what controls if the light is on or off?
 

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My understanding is that there's a keyed on wire running to the switch. That doesn't mean the choke is open all the time or that the light is on all the time. If your choke light is on all the time or the choke is engaged all the time, somethings wrong. I haven't pulled open the thermostat or the electric choke - but my assumption is that before a certain temp is reached the choke is closed by default. When it hits temp the thermostatic switch completes a circuit that disengages the choke. Or vice versa.
 

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It's not entirely clear to me, but here's what I see in the service manual. One side of the Choke lamp is connected to circuit branch 39, which I'm very familiar with, having just dealt with a shorting problem on it. 39 is hot with ignition switch on. The other side of the lamp is circuit branch 78, which runs to the + side of the choke heater. I think somehow (probably via a relay) 78 is grounded with ignition on, engine not running; thus, there is a voltage difference and current can flow. Branch 78 then jumps to close to 12V when the engine is running. With +12V on both sides of the Choke lamp, there is no current flow and, thus, no light.
 

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Discussion Starter · #13 ·
It's not entirely clear to me, but here's what I see in the service manual. One side of the Choke lamp is connected to circuit branch 39, which I'm very familiar with, having just dealt with a shorting problem on it. 39 is hot with ignition switch on. The other side of the lamp is circuit branch 78, which runs to the + side of the choke heater. I think somehow (probably via a relay) 78 is grounded with ignition on, engine not running; thus, there is a voltage difference and current can flow. Branch 78 then jumps to close to 12V when the engine is running. With +12V on both sides of the Choke lamp, there is no current flow and, thus, no light.
and that explains why the brown wire from the alternator is in the EFE relay! The light blue choke wires are in there also, along with the coil wire for the carb base heater.
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