EDIT: Note updated information

This question must come up monthly, so I figured it was finally time to write a little tech article. Many folks use the wiper power feed, but this has problems. Simply using a switched power source, especially one that is hot in the ACC position, will cause the choke to open prematurely if the key is on but the engine is not running. Also, the combination of the always-on choke heater and the wiper load may blow the fuse.

GM used two different methods to power the choke, depending on the vehicle. Most used an oil pressure switch in the power line to the choke. This way, the choke doesn't start to heat up until the engine is running and there is oil pressure. On my 62 F-85, I ran a fused wire (20 A fuse) from the BATT terminal on the alternator to the switch, and from the switch to the choke. Very simple to wire and very clean. I like to use the Standard P/N PS127 (note updated part number) switch. The middle terminal works the OIL light, the other two are a normally open switch that closes with oil pressure. Use these to control the choke. If you have an oil pressure gauge instead of a light, simply use a brass tee fitting to connect both this switch and your oil pressure sender. The interchange part numbers are as follows:

Standard Motor Products PS127
NAPA ECHLIN OP6618
Airtex 1S6552
BWD S369
AC Delco D1825A

Here's the sender:



Here's the wiring diagram:



The other way is to use a relay that is triggered by the field wire on the alternator (brown #1 wire on SI-family alternators, for example). The field wire is only hot when the alternator is turning. This is how GM wired the stock G-body cars with electric choke when the gauge package was installed. Of course the down side with that is that the choke will close if you break the alternator belt. A typical wiring diagram for the second method is here:

 

What a great idea Joe, thanks

 

The choke on my Ford is factory wired off the alternator field like the above.
The once 'nice' thing about that if the alternator fails, and the alt light does not work, the choke will close. This causes the engine to run poorly and tells you there is a problem before the battery runs flat and strands you.
Happened to me when the alt brushes wore to nothing. After 25 miles of poor running, I finally looked at the amp gauge and it was on discharge. I got home fine
and fixed the alt. Amazing how I got that far I got with lights and heater on.

 

This is perfect timing, I am just finishing the top end rebuild on my 350, and am converting to an electric choke.

One question, I'm sure more will follow, but just one for now...

Does the oil pressure switch used for the electric choke need to be the same one that is on the engine behind the water pump, or in the same location? or could an oil pressure switch placed elsewhere on the manifold (even in a place that has nothing to do with oil) be used?

The reason for my question is this. I want to minimize the amount of wire needed, and hide as much of the wire I use under the air cleaner in order for a neat appearance, so I was thinking of patching into the alt wire by the back of the engine to an oil pressure switch mounted in a port on the drivers side rear of the e-brock, meant for something to do with coolant, then to the choke from there.

If the switch is somehow activated by the actual pressure of the fluid it comes into contact with, this probably won't work, but if it doesn't I am thinking I'll be ok. I just don't know how these lil switches do there thing.

Any help or clarification would be awesome, Thanks!

 

The port at the front of the engine above the water pump is the only oil pressure port that's readily available, so either the switch needs to screw in there or you need to run a hard line from that port to a remote location where the switch is located. Either way works, and I've used the hard line and remote switch for exactly the reason you asked. Of course, you can use the relay method and avoid the switch entirely. The relay can be hidden anywhere, such as under the lip of the fender.

 

You could hide it in plain sight by wiring it and mounting it just like the rear defogger relay (providing you have NO defogger...)

Here is mine (for heated seats) in upper left.
http://www.flickr.com/photos/robsalb...7602930020786/

 

Solved eaisely,
Put a common "Y" brass fitting in the oil pressure outlet of the block behind the water pump.
#2 thread your oil ine in one side for the guage and the factory sending unit as in diagram above in the other side of the fitting.
#3 clip a factory plug for an oil pressure switch from a old harness, place on sensor and run one wire to choke thermostat and the other to the alt wire so not to have too much wire exposed and you can get the best of all worlds and also have the safety feature mentioned above like on the ford.
Its easy to do just decide if its what you want!!
Good Luck and let us know!!
Rich

 

This is a great idea, and one that I've used with Porsche and VW builds since 1968. The only difference is that I use the hot ignition rather than the alternator (or generator). I do not want the battery connected to anything until I switch that way.

 

Thank you very much everyone

 

Would it also be possible to use the electrical feed formerly used for the Distributor Vacuum Control Switch?

 

Your DVCS is connected to your transmission so that your timing will advance when the car is in high gear.

Not sure if it would be a great idea to wire your choke up to that. Unless you only want choke off if you're cruisin' down the free-way

I previously had my wired up the way that joe reccomended, it worked great. (Now i have manual choke so i dont have to care about these new-fandangled electric chokes)

 

Yes, the feed wire (green or green and black, if I recall) should be hot when the ignition's on, and should be fine for this.

- Eric

 

As Eric noted, the wire from the trans is the ground side of the circuit. The feed wire to the DVCS is switched +12V. That feed shares a 20A fuse with the backup lights and the turn signals. You'd need to check total draw on the circuit to be sure it's adequate.

 

I stated how it is wired from the factory and proper not off the alt feed but the reg switched on wire as again factory.

If you all have other ideas this is fine. if you want it right and as if it was supposed to be do it as I explained.

Sending me e-mail about this wire and that wire are not what we are saying.

Take your chances or please listen to good sound advice

Why in the devil would you use a parking light circuit or interior light circuit to run your choke???

It just does not make any sense???????????

 

Thanks to Joe and everyone else who responded.

There is a great deal of info on this now!!!!

 

Joe: Your post on using the oil pressure switch to control the electric choke is slick. You mentioned that you have run a hard line from the oil pressure port to a remote location. Where is a good place to mount a remote sensor, and how do you hold it in place? I've got a 66 442 with a/c, and the alternator sits right on top of the oil port.

 

Hey Joe, I had a buddy ask me about this subject on a car he is working on. The carb. on the car was originally a Q-Jet with choke tubes and has been changed to a Q-Jet with Elec. choke. He wants to run a seperate wire from the ACC (not currently used)pole on the fuse block to the choke. I figured it wasn't a bad idea since the key had to be on to make it hot; any thoughts? I'm not sure what sending units he is using as the car has had several changes throughout the years.
Please give me your opinion and I will forward the info.
Thanks, Dave.

 

I think Joe answered this one already.
Why not use a source that is only on when the engine is running, instead of one that could be on at other times?

- Eric

 

Will the PS64 switch fit a BB olds 69 400ci engine??

 

Yes.

- Eric

 

Is there a wire terminal with 3 positions to plug all 3 wires onto the oil sender switch,,,you know,,like your headlight which does both high and low beam has one terminal with 3 wires in it that does the job. Is there one similar a person could use on the oil sender switch? Or do you just have to use 3 separate wires/terminals singly? Just want to do the best looking job possible. I bought the sender already.

Thanks,Mike

 

Thankyou

 

The original application of that switch on a Vega did use a one-piece molded connector, but I have not seen one of these available as a pigtail you could buy. I just use three separate spade connectors.

 

Thanks to Joe P as this Sticky was just what I was looking for to power my electric choke on my rebuilt QJ. The PS127 switch is available at NAPA under part number OP6618 for about $16.00 plus tax.

Tom
68 442 almost ready to start
70 F85

 

Nicely done, Tom. I see you even used the correct connector on the choke coil. Is that a headlight connector on the PS64 switch?

 

Hey Joe,
thanks! There are actually three seperate single connectors, I didn't have a spare headlight plug...I guess I could have tried the headlight connectors before installing the switch and we would know for sure if it fits the oil pressure switch? Choke connector is supposed to be from a mid 70's to 80's Chevy truck?

Tom
68 442 convt
70 F85 post

 

Hey guys, just wanted to let you know that you can use a headlightconnector for this application. I plan on wiring it up in the next few weeks.


20131026_170409_1.jpg

 

That's good info, thanks.

 

Hi, I had a couple questions about wiring this. I haven't done any wiring so any help would be much appreciated. I have a 72 cutlass.

Which type of fuse would I use? The glass cylinder type or the blade type fuse?

What type of wire connectors would I use for the alternator and oil light or oil pressure gauge?

Where do you hook into the oil light? On the fuse box? Would it still connect into the oil light if I have a oil pressure gauge?

What gauge of wire should I use?
Thanks

 

I used the blade type fuse with I think 14 gauge wire the connectors I just picked up at the hardware store

 

1. Blade or glass type, it shouldn't really matter
2. As Dave said, the hardware store should have crimp connectors
3. This question is confusing. You'll be powering the choke from the alternator
4. If you're using a pressure gauge you'll still need the PS64 unit but you'll have to split the hookup with brass fittings as was mentioned in this thread. Look at post #24 of this thread.
5. 14 gauge should be fine, as Dave said.

 

I am considering this modification on my 67 330 2GC 2bbl. There are two choke tubes on this carb. One runs to the choke and the other runs to the back side of the carb at the top of the air horn. Does the carb still need this tube with the electric choke or can it be blocked off?

 

I remember reading on edelbrocks site the recommend the radio wire. What are your opinions on this

 

No, they are to be disconnected. I believe that the internal orifice between the venturi and the choke coil chamber should not be blocked, as the air added from it has been considered in the design of the carburetor, but others who have done this one way or the other should be able to provide better information.

- Eric

 

For what, power to the choke? Why would someone do this. Go back and read the first post in this thread. That's how the factory wired an electric choke.

 

Yes power to the choke ireplies I asked for opinions as to what is wrong with wiring into the radio besides the obvious reasons. Yes I read how the factory did it but I'm also relayi g what I read and why it should/shouldn't be done and the pros and cons of it.

 

The choke is a constant draw once it's activated. There's a reason why the factory gave it a dedicated fuse and wire. Sharing a fuse with the wipers, radio, or whatever else people tend to use can overload a fuse and/or wire. I'll take GM's engineering over E-brock's for this any day.

Frankly, I wired the choke on my 62 in a few minutes using the oil pressure switch and a dedicated fuse off the BATT terminal on the alternator. Seems a lot easier than fishing a wire through the firewall.

 

Ok that's all I was wondering thank you

 

So to be clear, I can disconnect the tube that runs from the intake to the back of the carb and leave the port on the carb open.

 

Yes, the port on the back of the carb near the top is just an opening into the area inside the air cleaner, so that the hot air system can pull in clean air.

- Eric