Sparky’s got me. It’s the coil. Why?

[Don C]

Check what the resistance (ohms) from the + terminal to the case on your old coil is.

On your new coil, grounding the negative terminal when you check the voltage on the positive terminal will tell you what your actual working voltage to the coil is. Just don't leave it grounded for long with the key on.

 

[Twins]

Right. The red plug gives +12V so the people who put in the previous pertronix prolly removed the resistance wire.

I put in the new coil and re-created the previous situation and no fuses were blown so that took care of that.

Still, I dropped the extra +12V wire from the choke to the coil. I can’t understand why that was there. Everything worked fine that way.

Thanks all who contributed to this thread with helpful ideas/knowledge

Cheers!

PS: I measured the resistance of the coils and the primaries and secundaries of the old and new coil were the same. But one is broken. Strange?

Oddly Vinnie when I upgraded to a Petronix ignition I too found two 12 volt wires connected to the coil which I had not noticed before.  The car ran with either one connected but the tach did not function with one of them connected alone but it did so with the other.  So I left that one connected.

  Someone must have bypassed the tach circuit in the past in my case when they had a starting issue.  

 

[Vinnie]

The coil resistor wire will only show reduced voltage if there is a load on it. Older analog voltmeters will load it enough to show some reduction, digital meters won't load it at all.

People that don't understand how loads on a resistor reduce voltages think it is OK to use the coil wire to power the electric choke. The additional load reduces the voltage even further, usually leading to performance issues with the coil, as well as causing the choke to take too long to open.

Eventhough the car seemed to run OK last night, I did measure the voltage between the + and - on the coil with a running engine and it was about 7.5V. So the resistance wire must still be there. But from what I understand the Pertronix will give me a bigger spark on 12V which should improve combustion, right?

I prefer not to rip out the resistance wire. The only +12V I know of is the wire from the fuse that is now hooked up only to my choke.

If I wanted to draw 12V for my coil, what are the best ways of doing so?

 

[Fabrice]

To test the feed, I'd measure from coil + to a ground, not to the negative of the coil.

You should have KOEOF 12v, during cranking something around 8v and engine running above 12v.

A typical resistance wire would provide 9 - 6 volts KOEOF.

http://www.pertronix.com/support/tips/#a2

https://www.fordmuscleforums.com/galaxie-pages/520833-pertronix-should-run-resistor-wire-switched-12v.html

 

[Vinnie]

To test the feed, I'd measure from coil + to a ground, not to the negative of the coil.

You should have KOEO 12v, during cranking something around 8v and engine running above 12v.

Is the coil's negative not (near) ground?

And how is there a difference between cranking and running?

 

[will e]

To test the feed, I'd measure from coil + to a ground, not to the negative of the coil.

You should have KOEO 12v, during cranking something around 8v and engine running above 12v.

Is the coil's negative not (near) ground?

And how is there a difference between cranking and running?

The negative on the coil isn't a constant ground and is not good for measuring voltage.

You will see the drop in voltage during cranking because the load the starter is putting on the battery.

 

[Fabrice]

and while running your alternator is busy generating power.

 

[Vinnie]

The negative on the coil isn't a constant ground and is not good for measuring voltage.

Oh! Of course, because the distributor keeps cutting it it's not a constant current. And that is why Don C. mentioned testing the voltage with the negative temporarily connected to ground.

How long (in seconds or minutes) can a coil take a constant power of 12V? Does the coil damage easily?

 

[Don C]

The biggest difference between cranking and running is that during cranking the coil receives full battery voltage via the"I" terminal on the solenoid and not the reduced voltage from the resistor wire.

The coil heats up when energized. It's not easily damaged, but I wouldn't leave it energized for more than two or three minutes.