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Electric Choke Wiring on 4brl Qjet

I love my Chevy Chevette!
Posts: 5
Joined: 10/07
Posted: 10/13/09 03:05 PM

I have a '75 K20 and I am trying to hook up the electric choke. My chevy service manual tells me it is circuit #78 and a light blue wire but I cannot find it on my schematic. I also don't think it is on my wiring harness but am not sure since I cannot find it on my schematic. Can someone post an electric choke schematic or tell me where I can find it on my schematic. Thank you all.  

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Everything in my driveway’s a Chevy
Posts: 556
Joined: 08/09
Posted: 10/13/09 04:59 PM

the versions with an electric choke use a 3 terminal oil pressure switch.... they have 3 terminals...   2 verticals and one horizontal blade...   | __ |      

see the  2 vertical terminals..   one side is from the choke fuse or idle stop solenoid fuse.. that same wire also continues to the idle stop solenoid if you have one..

the other side terminal goes to the choke thermostat..

the bottom terminal goes to the oil pressure light...

how it all works... as this switch is used a lot ...

the side terminals ... are isolated from ground...  and are open without oil pressure...  when the oil pressure comes up.. they close... allowing power from one to go to the other...

the bottom of the 3 terminals.. is grounded to the threaded end without oil pressure..  this grounds the oil pressure light .. so where there is no pressure.. the lamp circuit is grounded and the bulb lights up...

the oil pressure switch wiring is dark blue..

the power wire from the fuse box could be  brown with a white stripe..   and on to the idle stop solenoid...

the light blue wire only comes from the side terminal of the oil pressure switch..

feel free to ask questions..   different years tend to have slight variations in the fuse box  to oil pressure switch power wire...

up in 79.. its seems they have used some 2 terminal switches also..

for other people .. this same switch is used on fuel injected cars also...  the fuel pump relay only turns on for a few seconds to prime the system while you are cranking the engine..  once the oil pressure comes up.. it runs on the pressure switch.. the fuel pump relay shuts off..   this should shut off the motor if the oil pressure fails..

hope this helps..  

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I have an SS396 tatoo
Posts: 442
Joined: 10/08
Posted: 10/14/09 07:18 PM

WOW I never thought of why the wireing was like that, but that explained it for me anyway. Now I know what is wrong with my truck.  

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