Need help identifying 12v wire for electric choke

Hey everyone! I am installing an electric choke on my carb and know very little about electrical. The manual that came with the choke says to connect the wire from choke to the yellow/black wire going to the wiper motor. As seen in the picture, there is a yellow and a black wire. Does this mean I can use either one? It needs to be connected to the ignition so it turns on with the truck

What carb are you using?

The choke power wire can be the one that went to the original choke coil. If that wiring is gone or in bad shape, run a wire from a fused ignition terminal in the fuse box (there's usually an extra) and to the new choke.

You can leave the wiper harness alone, there's no reason to tamper with that.

I usually just run a wire from the 12V IGN Terminal in the Fuse Box to the Choke. Works great. Just need to find a place to snake it through the firewall.

Shouldn’t there already be a wire that comes from the oil pressure sending unit? Unless it’s gone for some reason.

I only know because when I got my truck, the wiring was a disaster. Apparently the choke gets power after oil pressure is sensed, then receives power.

bucket said:

What carb are you using?

The choke power wire can be the one that went to the original choke coil. If that wiring is gone or in bad shape, run a wire from a fused ignition terminal in the fuse box (there's usually an extra) and to the new choke.

You can leave the wiper harness alone, there's no reason to tamper with that.

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1977 Rochester 2gc with an automatic heat tube choke originally

Truck82 said:

1977 Rochester 2gc with an automatic heat tube choke originally

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Yeah, I'd just run a dedicated choke wire from one of the extra ignition power terminals in the fuse box.

bucket said:

Yeah, I'd just run a dedicated choke wire from one of the extra ignition power terminals in the fuse box.

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Ok. It seems like the cleanest way to do it too

SIDE NOTE:

This Holley video (YouTube site posted below) helped answer questions I asked elsewhere, which is, how does a choke work?

The video indicates the power applied to the choke opens it [rather than closing it] gradually. So, just turning the ignition on, even if the vehicle is not running, will, slowly, open the choke.

Once the key is off, power is (should be) removed from the choke circuit and the choke should start closing again, as the choke bi-metal coil cools.

Based on the foregoing, you need a full 12 volts to the choke when the ignition is on. Accordingly, and as long as the supply does not compromise another circuit (e.g., the ignition coil), any protected (fused) circuit active with the ignition in run should work.

The circuit does not have to be active in start, since that's when you need choking down of the air mixture, and the power to choke opens it, letting more air in.

The closest and easiest 12V that I found is the + wire on the distributor. That wire only has power when the rig is running, and is less than a foot away from the choke. The wire that says "BAT".

The factory setup in the later 80's models used a two prong NO oil pressure switch mounted in the 1/8 NPT port right above the oil filter. You would run a 20A feed from an ignition source in the fuse box to the oil pressure switch, then out of the oil pressure switch to the choke. This switch makes it so that the choke begins to open only once the engine is running and has built enough oil pressure to close the switch.

^^^^ This or wire it up G body style there are a couple of problems with running it off just a keyed ign source. Also you are not supposed to hook them to the ignition coil( Distributor Cap) you are asking for a burned up ignition module due to low voltage. My preferred way would be . A four prong relay,terminal 30 to 12 Volt source at battery or large alternator post, terminal 87 to choke element, terminal 85 splice to alternator exciter wire,terminal 86 to ground. This will allow 12 volts to the choke without drawing amperage through the ignition switch,making it's life easier. It also only allows 12 volts to the choke when the engine is running,less chance of a draw on the battery,a no start or an overheated choke element from someone leaving the key on.FWIW some choke elements count on air being pulled across them by the engine running to not overheat and burn out.

IMPORTANT, regarding using the BAT connection at the distributor:

FIRST, many warn against using the distributor tap for power, citing that using the battery terminal of the distributor can starve it of power needed for a top performing engine.

This makes sense in that it’s indicated the choke requires a 20 amp circuit and will be operating the entire time the rig is running. The battery terminal on a distributor only has to provide enough power to create an arc on one spark plug at a time.

Back in the day, my old truck saw 7 amps at the stock points. I changed to capacitive discharge to drop the point amperage from 7 amps down to 2/10 of an amp, or 200 milliamps, to make the points last FAR longer.

SIDE NOTE: They lasted so long the rider lobe finally started causing the dwell setting to drop off to almost closed every couple days. At first, I thought the problem was, I hadn’t tightened the points well, but figured out it was something else when I made sure I did, and it happened a couple days later.

SOME Net searches indicate the distributor-coil only need about 3-5 amps to operate effectively. That means the stock wire there may well be too undersized to use as a tap source.

OTHER Net searches indicate HEI systems can use as much as 30 amps.

In accordance with the foregoing, it is likely the wire feeding the battery terminal of the distributor would need to be increased in size, if it is going to be tapped for choke operation.

If, for example, you had HEI ignition taking 30 amps, adding the 20 choke means you’d need a 6 gauge wire to handle the 50 amps drawn on the circuit by the distributor and choke.

For stock wire systems, that means replacing the wire between the distributor and the starter solenoid having 12 volts only with the ignition on with a larger wire.

SECOND, if your distributor voltage DROPS FROM 12 volts to, for example, 7 volts, as many systems do when you go from start to run, the key run position feeds the distributor via a ballast resistor, or resistance wire, so you WILL NOT get the full 12 volts the choke requires.

THIRD, just to be, electronically speaking, safe, if using a sending unit, the same applies - it should be verified the sending unit feed wire can handle the 20 amps the choke requires, and still provide power to the sender, for the gauge or light operation.

SIDE NOTES

For my 78, going to a larger gauge is less a problem. With headers, there is the matter of getting your hot wires past them, to and from the starter, without them being affected by the high temperatures. One way of lessening the problem is, fewer wires.

Since the hot to the starter solenoid is being used as a power buss bar for other circuits requiring battery power, circuits merely tapping battery power off the solenoid (e.g., fuse block power) can be moved to after market power access point, or points, at locations well above and away from the headers, that are more convenient to access and are otherwise no a potential hazard to the wires.

Circuit protection is still a must.