So would I test that by measuring voltage at the coil relative to ground as I crank and then return the key to ON? This system is solid-state rather than points, so would that make a difference?
It would be worthwhile to check the wiring diagram for that car. A ballast resistor drops voltage to protect the points. With solid state ignition there is no need to drop the voltage.
Yes, measure V from the + side of the coil to ground and monitor it while starting the engine.
No, most solid state ignitions have + side of coil to 12V.
In addition to the primary wiring (with or without a resistance wire), the igntion switch is a possible culprit.
The sources that I have run across re the OP’s car are confusing. This link
http://carbdford.com/fletch/tech/duraspark/duraspark.htm
indicates there is a resistor used on the RUN circuit to the coil.
When I retired I gave away a wall full of Motors, Chilton and Mitchell manuals as well as factory shop manuals dating back to the early 60s thinking that they were obsolete. Who woulda thought I’d ever want to unfold one of those road map schematics again?
I found ballast resistors listed on RockAuto for my car, and the ford shop manual has a section on replacing the “ignition resistor wire” which I’m guessing is referring to the same part.
I tested at the coil while cranking the engine, and one post (they both have +12V, so I’m not sure which is the “positive” post) dropped to around 6V, fluctuating a lot, and the other dropped to about 9V, again fluctuating a lot.
Upon further investigation, the positive post is the one that was showing about 9V.
On my Ford truck anyway there’s two connections at the coil, one is the power connection from the battery, and the other goes to the distributor points. I don’t think I’ve ever measured that one, but it would measure around 6 volts I’d guess with the engine running, depends on the dwell. It isn’t actually a DC voltage when the engine is running, it’s AC, but the meter would measure an average DC voltage. It’s the one I connect my rpm/dwell meter when I’m doing a tune-up.
If you have 9V on the other one, the positive input to the coil, with the engine running, that should be sufficient to get a good spark. It also confirms you have a ballast resistor in the circuit, presuming the battery is holding its voltage ok. You’ll have to do both tests at the same time, to confirm/deny whether you are getting a spark at the same time you have 9 volts on the coil. With 9 volts on the coil and no spark at the spark plug, that would mean a problem with the electronic ignition module, the pickup which determines engine rotation, a ground problem, or the coil.
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