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resistor or not for 12v sytem

J

Jim In NY

Member
hi all : I know this topic has been drawn out, tipped over and probably drowned by now , however, this is my dilema : changed the engine from a 134 to a 172 gas and while doing so converted to a 12 volt negative ground system... that said in the interim the original coil (for the 12v engine) was lost, misplaced or maybe the dog ate it but nontheless it's nowhere to be found. So, I cannot find a resistor inline with the newer wiring we did when converting so I don't know what coil I need to purchase to eliminate any point(s) or other ignition problems due to the wrong coil , etc. Just want the right part the first time !
 
NAPA IC14-SB is a "true" 12 Volt coil, needing NO external resistor.

Any auto parts store should be able to cross that number over to the brand they sell.

At the end, what matters is CURRENT through the coil and points.

After installing the coil, if you have access to a suitable Ammeter, with a fully-charged battery, measure the current in the primary circuit, (switch "ON", points closed), you are "looking" for 3-4 Amps, at the low end or below, there's too much resistance in the primary circuit, and spark will likely be weak, as you approach 4 Amps or more, there will be excessive coil heating, and point heating, burning, and eroding, a sign of too little resistance in the primary circuit.

Be ready and make the test, don't leave ignition "ON" for longer than needed to make the measurement.
 
I'm with Bob, use the NAPA IC14-SB or equivalent coil.
They are less than $15 here and you have less connections to
corrode, troubleshoot and worry about in the future. One and done.
 
The one nice thing about the resistor is that you can bypass it for hotter spark at starting.

When i first got my '68 F100 they had the wiring screwed up and it was real hard to start, fixed the wiring and it was noticeably better starting.

Whoever re-wired my 641 did it 'the right way' and it has the hot to start, run goes through the resistor.
 
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