1939 pickup Coil

[Fech]

Hello,
Please provide a picture of how the original coil is wiring.

Also, can a 6v coil be use in a 12v system?
If so, what can I do to prevent any damage?

Thanks in advance.

[JSeery]

Originally Posted by Fech

Hello, can a 6v coil be use in a 12v system?
If so, what can I do to prevent any damage?

Yes, if you use the proper ballast resistor. You first need to determine what ohm value coil you currently have. This is fairly easy to do with a voltmeter with an ohm setting. You want about 3.0 ohm in the circuit for 12v (about 1.5 ohms from 6v). So if you coil is say 1.5 ohms coil, you would need to add a 1.5 ohm ballast resistor.

As far as wiring goes, it depends on what you currently have and how you want it to end up. For starters, what year is the vehicle and what coil is on it?

[Fech]

Thank you for the reply!
Ford 1939 pick-up
We want to install the original coil but no sure how to wiring.
Can you please provide a picture of the car coil wiring installation?

[JSeery]

Here are the wiring diagrams. Keep in mind things can be changed all over the place on these vehicles. There is a dxl and std version of the wiring, the commercial (pickup) should be a standard, but my understanding is some of the later models switched over. One of the major differences is the generator used, the early std used a cutout on the generator. The dxl used a voltage regulator and some of the later std or commercials may have as well. It also could have been updated. So, need to take a look at things and see what you have. Can provide additional wiring help once you establish what you are starting with.

Another difference would be an ammeter or battery indicator.

The fuse/ballast resistor panel is located under the dash on the firewall. The ignition switch block is located on the steering column. A wire from the ballast resistor passes through the firewall and connects to the coil.

[Fech]

Thank you again.
We don't have experience with this wiring. Can someone please provide pictures of the actual card showing the coil, wires where are connected?

[JSeery]

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I provided two diagrams, the wire connects to the terminal on the top of the coil as shown in the diagrams. It is labeled primary terminal in one of the diagrams and is #12036 in the other diagram.

[Tinker]

Skip can convert your helmet coil to 12v.


The connection is dependent to ground. If you're pos ground, you run a neg line to the coil. If you're neg ground its a positive wire. Distributor is grounded to the engine.


A later "can" coil can be confusing (and not applicable, +/- in/out, the to wire always the opposite of the dizzy ground). Helmets are simpler.


stock 6v coil i'd use a 50s ceramic 6v reducer (look at 57 ford voltage reducers, cheap) on a 12v setup. Coil doesn't care about polarity really, less it's run wrong.... then it won't fire (like mentioned). Your stock ignition is setup to run about 4v at the dizzy (2v resistor under the dash for stock 6v (give or take, heat, etc...)) If you run straight 12v through the stock coil you'll burn the coil,points,condenser out in quick fashion.


Don't know how you plan to wire your system, but a new stock 6v wire harness is actually thicker wires and can handle 12v all day. It's just small things that you need to change... like gauges, bulbs, ignition. Adds up also.




.

[JSeery]

If your converting to 12v, the generator will have to be addressed, alone with the gauges and the coil. Most of the rest is not too big a deal (lights, etc). The starter will work on 12v, but it will "hit" a lot harder into the flywheel and turn over faster. Can be an advantage, but can also break the Bendix unit.

[rotorwrench]

There may be an adapter involved. The adapter fits on the distributor (helmet type) and a regular can type coil can be used. The engine can also be converted to the later two bolt (1942 to 1948) type distributor referred to as the crab or rabbit ear types depending on what configuration it is in.

We would need to know if it still has the original distributor or not. JSeery provided illustrations of what they look like in post #4. If it's original then we would need to know if it has an adapter or not.

The original ballast resister would not work well with the 12-volt system. If a can type coil is used then a 1.3 to 1.5 Ohm commercially available ballast resister can be used. If the coil is marked for 12-volt, then no ballast is required. Polarity of the system has to be observed with an ignition coil. A negative ground system would require normal connection of a coil with negative to breaker and positive to ignition switch. Positive ground is generally opposite of that since the polarity it reversed from the norm.

[Fech]

The pickup is working with 12v, but with not original coil. We want to install the original but is 6V.
Thanks to all for the help.

[JSeery]

Check the resistance of the original coil and add the required ballast resistor to get the total resistance in the circuit in the 3.0 ohm range.

The original Ford bulletins list the total resistance in the original circuit as 1.0 to 1.35 ohms. If the original coil is around 0.6 ohms then the original ballast resistor would need to be in the 0.4 to 0.76 range. I believe they tend to be in the 0.5/0.6 ohm range. You have to keep in mind that the resistance of ballast resistors change with temperature, they get hot in use and the resistance changes.

I have never done this! But in theory you could set up a 12v input to a 6v original style coil by keeping the total resistance in the 2.0 to 3.0 ohm range. Using 0.6 as the original coil resistance a ballast resistor of 1.4 to 2.4 ohms should work.

However, there is the polarity issue. Reversing the polarity on a coil can reduce it's output up to 80%.

One option would be to have the original coil rewound to 12v specifications. Skip is one source for that service.