The Stovebolt Site Forums The Shop Area The Electrical Bay switched lead in the engine compartment

I think I know the answer to my question below, but I am hoping that I am wrong.

I want to provide power to electric chokes when the ignition switch is on. This is a 6v system and two 12v automatic chokes. The 12v chokes are supposed to be able to work with 6v leads (they simply warm up more slowly). The recommended gauge of wire for the chokes is 12 gauge.

The correct way to do this is to connect to the switched side of the ignition switch, but my switch is overpopulated with original and accessory leads. I would like to find a alternative, switched connection point in the engine compartment (first choice) or under the dash (second choice).

The ideal switched source of power in the engine compartment would be the switched lead into the coil, However, the wire to the coil is 18 gauge. Am I correct that connecting the 12 gauge choke wire to this lead at the coil would overload the 18 gauge wire to the coil?

Is there any other ignition-switched led in the engine compartment?

If I have to connect behind the dash and do not want to connect to the ignition switch, is/are there other switched leads under the dash? Maybe at the ammeter? The light switch is hot all the time - right?

Thanks for any corrections, suggestions, advice, and sarcasm.

Tim

Tim,

I don't know the details of what you are doing so this might be all smoke! If you are using two carburetors, I have often read that only one needs to be equipped with a operating choke!

From your post, I assume replacing the coil wire with a heavier gauge would be a major task...it's probably inside a nice OEM loom or something.

The ignition (coil) is about the only thing switched by the key in the engine compartment. I'm not sure what would happen if you attached your choke wire to the ARM terminal of the voltage regulator...this wouldn't be powered until the generator started to output, a 'faux switch'.

My bet is you don't have a generator! probably replaced it with a nice 6 volt alternator.

Are you sure your coil wire is 18 gauge...that is pretty small for any device. The books says it's only good for 3 amps. I don't know what your choke coil draws. 16 gauge is good for 6 amps, which I would think might be more of a standard gauge for the smallest wire under the hood! That's my two cents, good luck.

Stuart

Stuart,

Thanks for the suggestions and questions.

I'd like to set up the choke on both carburetors for a couple of reasons: it would be simple to wire and then I would not have to disable the choke on one (or remove or block open the choke flapper). On my old dual Rochester set-up, I only connected one of the manual chokes and it started fine.

This truck is set up with original 6v generator and voltage regulator and a wiring loom that supposedly meets original specs (for wire gauge and wire color). The lead to the coil is supposedly 18 gauge and it is a relatively thin wire compared to other wires (it's about the thinnest that I can see). I was wrong above, the carb specs call for a 14 gauge wire for 12v to both carbs.

I like your idea of using the ARM terminal on the voltage regulator. Could this do any harm?

Now, this next question will prove I am electrically disabled: if a 14 gauge wire is needed for a 12v set-up, wouldn't a heavier wire be needed in a 6v set-up? Or, will the draw be lower for 6v and it will take longer for the choke to fully open and the lower gauge wire would be OK?

Tim

Tim,

This will be one electrically challenged member to another. Because the choke coils are a resistive load, I don't think they adhere to the common practice of twice the draw for half the voltage, so a 14 gauge wire would probably work fine for both carburetors.

I'm hoping some carburetor expert will jump in here because I don't think your rig will work with both carburetors choked. Maybe this would work if the full choke shut position was only half closed, I don't know.

Because the choke heater coils are sized for 12 volts, they may stay on way to long for practical applications with only 6 volts.

I don't know if tagging a choke power lead off the regulator ARM terminal would work. I'll bet someone that knows for sure will be along shortly.

The absolute proper way to wire this would be to determine the exact wire size required, fuse it and run it to the ignition switch. Not much help from me, huh!

Stuart

Tim, a few of the switched points that could be picked up on would be heater blower motor, one side of gas guage, radio connection, an I think there are some on the headlight switch.

As far as the wire guage question, I can reason it both ways. I think the large wires on 6V is more to get maximum current for the starter. The formula is current (Amps) = Voltage divided by resistance of the circuit.

If you wire both chokes, the resistance that the source will see will be less than one of the chokes by itself. As I reason it out in my head, If the power to each choke comes from the same power source, and the other side of the choke is to ground, essentially, they are wired paralell to each other. The total circuit resitance would be one over the combined recirocals of each individual choke coil.

I would get an aux. fuse block & put it on the firewall inside on the left side. Run a 10 gauge wire to it from the switch & have a fuse for each add on acess. like radio, heater, & choke. Volts is pressure. You need larger wire for 6 volts because you have less pressure. If you run both chokes off 1 wire you probably want 12 gauge, unless it's a short distance then 14 would work. Each one would work off 16 gauge. Set the chokes on the lean side. I havn,t ran dual carbs in so many years I am not real familiar with them.

darn, Greg. This is a holiday. Not a day for mathematics and physics.

Yes, the inside points that you mentioned are my 2nd approach - I'll go for the heater blower feed because it is the closest and easiest to reach. What do you think about attaching to the ARM lead on the Voltage Regulator?

Here is one instruction that I have found through a web search: "The proper place to hook an electric choke is the 'Stator' lead of the alternator." Is that functionally the same as the ARM lead on the voltage regulator?

Tim

Tim, that was a mad rush of info I learned 30 some odd years ago and hadn't used since. I don't have an answer to your connection match question. You said that the ignition switch was "heavily populated". What all do you have there?

The switched pole on the ignition switch most likely has the radio, heater, glove-box light, and coil. (I did not want to trust my remembering to turn those things off, if I had left any as unswitched devices)

you could use the power from the coil to power a relay that is connected to the battery with a fuse of the right size then to the chokes. that's how i did it on my '73 with a edlbrock 1406

Why not use the setup that the factory designed, with an oil pressure operated switch? A fused wire from any convenient 12V source, such as the battery cable connection at the starter is run to one side of a normally-open switch that's closed when the engine starts by oil pressure. The other side of the switch feeds the choke(s). If the engine stalls, the chokes quit heating, so a restart isn't a problem. All the factory electric-heated chokes use somer sort of interrupter circuit in case a cold engine stalls. It's also idiot-proof, so you don't forget to turn the heater on when it's needed.
Jerry

I prefer to not use a relay but a 6v relay would be a possibility (triggering the relay with a lead from the coil).

After considering the suggestions posted above, I will first check to see if the ARM lead on the voltage regulator "acts" like a STATOR lead on an alternator-equipped car (a location often used for 12v chokes leads). This would be in a good location and would have enough power (I will be using a 12 gauge lead). Most likely I will use an in-line fused lead. Does anyone have any comments regarding this "solution". I will test this empirically (tonight) but if this is useless, it would be nice to know in advance.

My second choice will be to go under the dash (with a fused lead) at the power side of a high-draw accessory (heater switch, probably).

My third choice is to do the rational thing (that I was trying to avoid) and connect to a switched post on the ignition switch (again using a fused lead).

Thanks,
Tim

Tim,

You probably already know this, but your second choice and the third choice are basically the same...just a different location in the same circuit.

Anything that is switched is done so with the only switch available, the ignition switch. If your heater is wired to turn off as you kill the engine and leave the truck, it is accomplished with the ignition switch.

What I'm saying is that the powered side of your fan motor is only the other end of the wire from your ignition switch. I thought the ignition switches had two terminals, both powered when the switch was ON. This allowed the contacts to share the load and allowed for more 'leg room' to attach wires.

I will be interested in your findings on the ARM terminal of the regulator...in my pea brain, it sounds like it should work!

If your truck burns to the ground, blame Joker!

Stuart

The ignition switch is not rated to handle more than the heater, dash lights and ignition. That is why the factory instruction for the radio call for connection before the switch. Your best option is to use a relay that is activated by the coil supply or ignition switch. Power the contacts from a fused supply.

The armature current is monitored and regulated by the regulator. The regulator would not see the current tapped directly from the armature and you could burn out the generator.

Fred,

Your comment about the voltage regulator makes sense...that sort of puts the skids to any connection to the ARM (gen) terminal as it would be before the current relay.

Stuart

Tim
I would run a single wire two steps heavier than the one supplying the ignition switch. the other end would be a busbar or as wrenchbender suggested( a better ideal) a aux fuse block. Goal 1 - switched power, Goal 2 - get it away from wire cluster of ignition switch, mount anywhere you can access it and be out of sight. Also put a fuse or fuseable link inline between ignition sw & aux box.

Suggestion 2
Put a relay to ign sw and run power straight from battery to aux panel. Wire like a cooling fan relay. 30a is pretty standard , I have seen special applications up to 75a. Still meets both goals. This link shows how a relay works and is wired. I suggest the 4 wire EASY to wire relay and pigtail usually about $10 total

http://www.bcae1.com/relays.htm

Good luck
Brad

The oil pressure switch sounds like the hot tip to me. He's not talking about the sending unit. This is a switch that makes contact when there is oil pressure. You can tee into the outlet where your sending tube is.

Jerry & Cletis,

Could you post a link to one of those oil pressure activated switches?

It sounds like there would be at least two poles on the switch. Are the switches rated at different amperages (or watts)? I can find no information on the 12v amperage draw of a 1983 Motorcraft Model 740 2-Barrel carburetor. All I know is that the instructions say to use a 14 gauge lead from both carburetors to the ignition "on" switch.

I still have to drill-and-tap one of my oil filter fittings (1/2" NPT) for the oil sender adapter fitting (1/8" NPT). So, I could easily use a T-fitting (as Jerry suggested).

If I go with a 6v electrical relay (Hella and Bosch are the only two I can find), if the relay is triggered from the ARM pole on the voltage regulator, would that provide the stall interruption that Jerry describes: " If the engine stalls, the chokes quit heating, so a restart isn't a problem. All the factory electric-heated chokes use some sort of interrupter circuit in case a cold engine stalls."?

Thanks,
Tim

Your ammeter is connected between the battery and the rest of the truck electrical systems. Apart from the starter and the horn, all loads go through the ammeter. If you connect a switched load directly to the battery with a fuse as suggested, that load will show up as a current in the charge direction. In other words you can end up with a discharging system and not even know it. If you need a supply you should tap off the load side of the ammeter.

Tim, the best I could find was a picture of one on the 6066gmcguy web site, about the middle of the page. A google search tuned up a bunch of modern cars that use them but nothing about the type and the turn on pressure. You might be able to contact Jolly and find out the application of the one he used.

???

http://www.pegasusautoracing.com/productdetails.asp?RecId=88

http://www.corvetteparts.com/details/iid/23022101.htm

http://www.irvansmith.com/scart/fuel-pump-shutoff-switch-p-1702.html

http://www.jegs.com/i/JEGS/555/11200/10002/-1

http://store.summitracing.com/partdetail.asp?part=hly-12-810 (this page has a link to technical specs - finally)
http://store.summitracing.com/partd...T&N=700+-147154+115&autoview=sku

Tim,
looking at the diagram in the last link, that is of course for running a fuel pump. In your case, you don't need to bother with the NC contact attached to the solenoid as it would not serve any purpose.

The load side supply of the ammeter is actually connected to the BATT terminal of the regulator. You could run a connection under the hood to that terminal, use an inline fuse and feed the NO terminal on the pressure switch.

truckernix,

Yes, thanks. That is what I intend to try. I appreciate your follow-up. My only concern now (I think) is the amount of current that the pressure switch can handle (7.5 amps, I think). I still do not know the amount of current that two chokes will draw. If I blow fuses or burn-out the pressure switch, I'll get a new switch and use a relay. I am trying to do this as neat-and-simply as possible.

Jerry and others have convinced me that the oil-pressure switch is the way to go. I am now on hold with Holley technical support to see if they can give me more info on the chokes and the switch.

Tim

OK, Holley says the choke draws about 5 amps (12v) and the oil-pressure switch will handle that. The switch would most likely not handle the draw for 2 chokes (at 12v). I did not even get into the 6v issue. He said just connect the chokes to the ignition switch.

New options (in order of simplicity and functionality):

1. Choke one carb, using the oil-pressure switch (12v, 7.5 amp).
Why not: This might not work with the choke's 5 amp draw at 6v?

2. Use a 6v 20 amp relay (if available) triggered by the appropriate pole on the voltage regulator and powered by a fused lead to the starter or to another heavy power source in the engine compartment.
Why not: Is such as relay available (I'll check with Jolly - neither Hella nor Bosch have their ratings on-line)?

3. Use a fused junction block, fed by the switched lead on the ignition switch.
Why not:
(a) The choke would be heated as long as the switch is open (even if the engine stalled) - not desirable but it would work. (b) This might then result in an additional 20 amp draw on the ignition switch - not desirable?

4. Use an oil switch to trigger a 6v 20 amp relay.
Why not:
(a) This is the most complex (most fittings, parts, and wires).
(b) Costs a little more than any other option.
(c) Depends on finding a 6v 20 amp relay.

Any of the fuel injected Chevy V-8's will have a 3-pole pressure switch that mounts in a threaded port just above the oil filter. Two of the terminals are the normally-open fuel pump switch leads, and the third one is a ground for the oil pressure idiot light. You can use just the N.O. terminals to connect a straight battery voltage source to the choke(s), and it interrupts the circuit anytime the engine stops. Safe, positive, and it doesn't need to go through the ignition switch. I would reccomend using an inline fuse of about 20 amps on the hot side, just to guard against a short circuit anywhere.
Jerry

Edit: Forget about the rated current capacity. I've used those switches to carry 15 to 20 amps without any problems! They're way over-engineered!
Jerry

Edit X2: The turn-on pressure is about 7 lbs. It's the same as the pressure necessary to turn off the idiot light for low oil pressure.
Jerry

Thanks. I'll check out fuel-injected V-8s. If I find a part number, I'll post it here.

If anyone else has more specific information on model/year/engine (heck, or even a part number), please post it here. It will speed up my searching.

Tim


From a quick search on Corvettes from 2000 backards:
Two pole pressure switch:

http://www.napaonline.com/NOLPPSE/(S(bhtqt1bt2dwwo245xlpybxzn))/Detail.aspx?R=MPEOP6616SB_0209176328

http://www.napaonline.com/NOLPPSE/(S(bhtqt1bt2dwwo245xlpybxzn))/Detail.aspx?R=ECHOP6616_0208780933

It would be nice to find the specifications, but it looks like this is a good candidate.

This is cheap enough that I'll simply give it a try.

Just in case someone finds this post and is interested in using an oil pressure switch to control the feel of power to electric chokes on a 6v or 12v system, here is the final solution:

NAPA: MPE OP6626SB

I have this now working to control two Carter-Weber Motorcraft 740 2-barrel carbs on a 6v 261 engine.

I had to try several two-pole and three-pole switches before I got one that switched appropriately for this application. It switches on at about 4 psi (rated to switch on at 2-8 psi).

Tim