At the positive wire or the positive terminal on the coil?
Either one as long as the wire is present.
The positive terminal on the coil has practically no voltage to measure which makes sense since it's not connected to anything.
Correct. Not connected means no voltage at all.
However, the positive wire has 11.46 volts when the key is in the on position. Drops to 8.6 when cranking.
Sounds good.
Not sure what difference this would make for generating spark
Could make all the difference in the world either while cranking (bad relay) or while ON (bad wire) because the Brown wire as you know is directly connected to the Red w/green wire on the coil's positive side.
The purpose here is just like removing a tachometer wire (you don't have a tach, do you?) when testing a no-spark condition. Just to eliminate anything related as a possible culprit. So disconnect the Brown wire for now even if it doesn't make sense.
This does absolutely nothing, even in my '67 that runs and drives perfectly. Negative side from the distributor disconnected, jumper wire from the negative coil terminal to the negative battery post. Positive wire hooked to the coil, key in the on position, no spark generated by the coil wire when grounded.
Unless I'm somehow doing this wrong.
You might be.
It does not generate a spark when grounded. It generates the spark when you remove the ground. But first it must be grounded for you to remove, or "un-ground" the terminal. This is precisely what the points do in a working engine. Each time the points separate the coil generates a spark.
You can get the real theory behind this from the others. I only know the real-world situations and not the theory behind the magnetic fields and such.
But it should have worked on the known-good coil, so you need to watch it while you un-ground it.
And don't leave both the positive and negative connected to the coil for very long. While I've never had an issue with it, this is what some report as having overheated the coils pretty quickly. I've run my factory and a Ford Racing coil like that when I was having power issues and both are still working to this day. But we can't ignore others that say they overheated a coil. No way to know how long they were left connected to the battery.
Same thing as leaving the key on for a half hour while working on other things. Not supposed to do that.
A little more information, I took the coil out of the '73 and swapped it into the '67. '67 starts and runs fine and I can get the spark by having the key on, the + and – terminals of the coil connected to the wiring harness and distributor, and grounding the coil wire to the smog pump case. The coil checks out fine on the '67.
Great info! This means that something is wrong with your wiring or your distributor. As has been discussed.
If it works on one vehicle then it's not the coil. The previous test was just to see if the coil works, but you did it by swapping it into the running vehicle. Same result, different test method.
'73 seems to generate no spark whatsoever no matter what I've tried.
Keep checking the distributor.
If you do a variation on that previous test by prying open the points with the key ON you should get a spark both at the coil and probably a small one at the points each time you pry them open.
Obviously you need to either make sure the points are closed when you start the test, or fiddle with things enough with a metal tipped screw-driver or whatever so that the points are grounded between each other, and then not grounded. Each time they are grounded then not grounded, you should get a spark.
If not, then either the Black wire to the negative side of the coil is bad, or the condenser is bad. Could still be other things, but those are the most likely at the moment.
But in the meantime, are there ANY other wires on the coil?
Paul
