Nick Bernier

Hi Guys,
I really appreciate all the help I've received here, but need some more. I have the dual point distributor. I get 12.43v at the batt. With the ignition switch ON, I only get 11.44v at the high side of the resistor in front of the coil. I get 6.91v on the coil side of the resistor. On the + terminal of the coil, there is another green wire which according to my wiring diagram goes back to the ignition switch. My diagram is not very clear, but it appears to show a brown wire from the ignition switch to the resistor, green from resistor to coil, and green from coil + back to ignition switch. First question is why the drop of one volt on the ignition switch side of the resistor? Am I missing something, or is it just voltage drop from old wires/connections? Second is: Why are they sending 6.91v back to the ignition switch? Would this low voltage cause a weak spark? I have the NCRS wiring diagram book, but it doesn't detail the ignition switch itself. Also, I can't find the wiring diagram for the radio??
Thanks for any help,
Nick

Avispa

What else is switched on when the ignition switch is turned on? You may have some current draw through the voltage reg/generator and anything else on like the radio. That would account for a 1 volt drop through the wiring harness. The second green wire to the coil side may go to your starter solenoid. There's usually a ballast resistor bypass when the starter is cranked to keep the voltage at the coil up when cranking.
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Nick Bernier

I get it. It's not sending 6.9v back to the ignition switch, but that's a path for a full 12v to get to the coil during cranking. It would be helpful to have a diagram of the ignition switch internal switching. Nothing else is ON. Only the gauges are powered up.

toddalin

I would suggest that while you are checking voltages, your points are closed. The combination of the ballast resistor and resistance of the coil form a voltage divider, and that's why you see 6.-- volts on that side of the coil.

Of course if the points are closed and you have 6.-- at the coil/back side of the resistor, the system is under a load and this is reducing the voltage on the front side of the resistor, at least to some extent due to other resistances along the path (e.g., length of wires/connectors).

Nick Bernier

WOW. You guys are good. I disconnect the coil/distributor and voltage back to 12.4. I feel a lot better when I understand why things are the way they are.
Thanks,
Nick

69427

Does the OP's '57 have the starter/ballast bypass? I was under the impression that the bypass first came on board in '58. The OP mentions "another green wire" going back to the ignition switch. My impression is that his wiring possibly does the same ballast bypass, but the ignition switch does this in the cranking mode.

I welcome correction if I am mistaken.

Nick Bernier

The wiring diagram I have shows the second green wire on the coil going to the ignition switch. I'm guessing it's what Avispa is saying: to supply 12v during cranking. I don't have a diagram of the internal switching of the ignition switch.

Thanks,
Nick