Duraspark concersion coil wiring question

390Fastback · Mar 6, 2018

So I've got it all done, can get it started and when it does start it runs better than it ever has under my ownership. BUT.....no spark on start. I have spark on run obviously but that's it. I found the brown w/pink that has 12V power in start but nothing in run, then I found a red with no trace that has 6.8V in run and nothing in start. Could not find the red w/light green as mentioned in the write up though.

So the question is, can I tie these two wires together? Or am I looking for a fire??

Ok I just found an electrical drawing on here that shows the red w/green and brown w/pink intersecting at a node, so I should be good with tying these together....I hope. Still makes me wonder why I have no power in run at the brown wire. And I'm a little concerned about the low voltage in run from the red wire......

390Fastback · Mar 7, 2018

Figured out the low voltage thing, with key on engine off that's normal. I've looked at enough drawings, i'm just going to connect everything and see what happens. The ignition switch diagram says it should work, other drawings say it will work. I have a couple other things to do with it this weekend, I'll post what happens..... fingers crossed!

RonD · Mar 8, 2018

Back when there were still points in a distributor there was a ballast resistor or resistor wire, that was used for "+" terminal of the coil, this would lower the voltage at the coil while engine was running, Alternator 13.5 to 14.9volts, so coil would see about 9volts, which is plenty of spark for a running engine.
Coil didn't overheat and lasted much longer running at 9volts

But for start up there was a problem, the starter motor drops system voltage to 9-10volts when cranking, you add resistor to that and coil gets about 4volts, so very weak spark, especially for cold start.

On the older Starter Relays(solenoids) there was a 4th small post, it was labelled with an "I" for ignition, and there was a wire from it to Coil "+"
When Starter was activated the "I" post also got voltage, 9-10v while cranking, so coil got full power.
When starter motor was off "I" was disconnected so only resistor voltage was at the coil.
Why the 4th post, why not just hook the wire to starter motors post?
Because other end of "I" wire, at the coil "+", has 9volts when engine is running and that can feed to starter motor causing it to turn, also melt the small wire, lol.

With electronic ignitions there was some crossover, because old style coils were still being used, newer coils can run fine with 13.5-14.9volts

So they ran two wires from ignition switch to the coil "+", one had full voltage only in START position, the other ran thru resistor and only had voltage with key in RUN position.

So yes, in answer to your question, you found both of these wires, and as long at both have no voltage in opposite positions then you can connect both to coil's "+" terminal

390Fastback · Mar 8, 2018

Awesome, that's what I thought, I just needed to hear someone else say it. And that's pretty much the explanation I found also. Thanks!!

Duraspark concersion coil wiring question

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