Is a ballast resistor necessary on 6v system? I'm getting 3v at the coil. I had a guy that's a model A restorer wire my car, maybe he thought it was 12v?. I'm thinking it may be unnecessary.
You don't say what distributor or coil you have. Let me suggest two possibilities. a) stock 32-41 flathead V8 distributor with its stock (mounted atop the distributor) six volt coil. This MUST have that little resistor in your pic wired in series from the ignition switch to the neg side of the coil. This is meant to drop the voltage to the coil from six to roughly 3-4 volts. b) aftermarket 8BA type six volt coil (common cylinder shape - internally resisted). This coil takes the full six volts to its negative side. Under this scenario, you would NOT want an additional resistor in line to this coil. Leave the Ford resistor under the dash but bypass it with the wiring to the coil.
Dead coil? An ohmmeter can tell you if you have open windings on the primary and the secondary windings.
I'd guess that you could shunt the wiring to bypass the resistor, at least temporarily, to troubleshoot your no-spark condition. Just don't leave it that way as a permanent fix if your ignition system does in fact require an external resistor.
If you are running the stock '37 distributor and coil, which is mounted on the top of the distributor, you need that resistor. If your distributor has been outfitted with a modern remotely mounted 6 volt coil you don't need or want the resistor. The old stock coil may be bad. Do you have voltage in and out on the coil? Have the points and condenser been replaced recently? Fried condensers were a bit of a common illness on these engines. You can buy an adapter to remotely mount a modern coil from most suppliers of antique Ford parts. If you go that route be sure to use the condenser that matches the coil and eliminate the resistor. I prefer to use the stock setup. Properly working that makes one HOT spark.
When I wired the Jesse Lopez car I left the factory ballast that is in the same location as yours and added the proper 12v ballast inline. Car runs just fine. Yes, 3-4 volts at the coil doesn't sound like much but that is what that system was designed to run on. Make sure there is voltage at the coil with the key on... if there is check the other terminal while cranking the motor.... the light should flicker. If it doesn't, usually means you have a problem in the points/condensor/wiring. BUT !!! A shorted coil can be the culprit also.
I had a 39 distributor with a bad coil. I removed the coil and coil cover. Drilled one small hole in the flat bottom piece into the brush holder and fished in the conductor of a solid core wire. Stuck a drill bit into the brush hole to flatten the wire. The wire from the points side of the coil goes to the brass tab used for condenser ....Low bucks remote coil conversion.
I believe the stock Ford coil is around .6 ohms primary resistance. Generally speaking 6 volt system coils are 1.5 ohms for decent point life. So Ford added a resister to give more resistance. but I think the real reason is the ballast has less resistance when cold....So when you crank the engine there's more spark energy to make up for battery voltage drop when the starter is engaged. Then when the engine runs the ballast gets hotter and resistance goes up to protect the points.....Kinda like how 12 volt ballast systems work..
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