How to wire up an electric choke

bill

bill

Comic Book Super Hero
Jul 11, 2008
2,556
38
southside va/lake gaston
update.....I have installed the oil pressure switch that Joe recommended. However, when I hook up the oil pressure warning light wire to the center terminal on the OPS, it stays on when the ignition is off and goes off when the motor is running. Any explanation as to why? The choke heats up fine as intended, but I still want the oil pressure light to work as well.
 
Dayzedandkonfuzed

Dayzedandkonfuzed

G-Body Guru
Feb 9, 2010
715
93
Anglemont, BC
The light should be on with key on, motor not running. If it's on when your key is off, you aren't on key switched power to the switch.
 
bill

bill

Comic Book Super Hero
Jul 11, 2008
2,556
38
southside va/lake gaston
Umm....not sure I follow what you mean....Wait.. You are saying that the voltage isnt coming from the key switch, but from someplace else? Yeah...I got that much, but if the switch is normally open, no voltage should be getting to the other terminals from the alternator wire except when there is oil pressure. But, under that situation, the light would come on when the engine was running and there was enough oil pressure to the switch to close it.
 
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Dayzedandkonfuzed

Dayzedandkonfuzed

G-Body Guru
Feb 9, 2010
715
93
Anglemont, BC
The oil pressure switch is only open when there is sufficient oil pressure. That's why the light comes on when you turn the key to on, but goes out when you start the car. So if you have constant 12v at the switch, your light will not turn off with the key.
 
bill

bill

Comic Book Super Hero
Jul 11, 2008
2,556
38
southside va/lake gaston
I think you may have it backwards......Oil pressure switches are normally open....and only CLOSE with pressure, in most cases. That is the only way this set up will work for an electric choke. In my book....open means no current flow...closed means voltage....your results may vary...o_O
 
Dayzedandkonfuzed

Dayzedandkonfuzed

G-Body Guru
Feb 9, 2010
715
93
Anglemont, BC
if your oil pressure switch were closed with oil pressure, your light would be on with oil pressure. Now, the choke terminal will be closed with oil pressure, but the warning light side of the switch will be open with oil pressure. This is where our confusion is.

Regardless, you need key switched power to the oil pressure switch, and with what you have posted, you must have constant power to it.
 
truracer20

truracer20

Master Mechanic
Feb 16, 2014
493
18
western PA
If the light stays on with the key off then you have constant 12v to the switch and not key switched 12v as it should have.
 
Dayzedandkonfuzed

Dayzedandkonfuzed

G-Body Guru
Feb 9, 2010
715
93
Anglemont, BC
Think of it as 2 switches operating oppositely, like a 2 pole toggle switch. Only 1 will be on at any given time, either your choke, or your warning light.

So technically, this oil pressure switch cannot be classified as "normally open" OR "normally closed," because 1 terminal is normally open and the other is normally closed. With this switch sitting here on my desk, the light terminal would be closed, the choke terminal open.
 
bill

bill

Comic Book Super Hero
Jul 11, 2008
2,556
38
southside va/lake gaston
I think you may have it backwards......Oil pressure switches are normally open....and only CLOSE with pressure, in most cases. That is the only way this set up will work for an electric choke. In my book....open means no current flow...closed means voltage....your results may vary...o_O
if your oil pressure switch were closed with oil pressure, your light would be on with oil pressure. Now, the choke terminal will be closed with oil pressure, but the warning light side of the switch will be open with oil pressure. This is where our confusion is.

Regardless, you need key switched power to the oil pressure switch, and with what you have posted, you must have constant power to it.
Ok...I just went out to look at the setup again. I wasn't aware that one terminal is normally open, one is normally closed and one is constant. I had my voltage wire on the normally closed terminal and the wire for the light on the constant terminal. I switched the the voltage wire to the normally open side, and switched the light wire and choke wire...and what do you know...it all works fine now. I will go back to my corner and eat crow ....lol Joe's picture isn't as detailed as it could be...I'll take a picture of the switch wired up. White wire is to the alternator, red is to the choke, and the other is to the idiot light.
 
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