I have a 1948 8N that has been converted to 12 volt negative ground with alternator. I have 1247XT Pertronix electronic ignition. It tan fine until recent engine rebuild. Upon reinstalling engine i am having trouble with ignition so am entirely replacing it with new 1247XT and new coil. Summit Racing is telling me if i use their Flamethrower coil w/3 ohm internal resistance, i don’t need ballast resistor. I have read Bruce Haynes’s posts on this subject and his 75 Tips For N Owners Based on what i read there, Summit Racing’’s advice does not sound correct and coil will overheat with high resulting amperage. Is it?

To expand a bit upon my previous reply, the Flamethrower is a round can coil, so no external resistor is needed. If your existing electronic ignition uses a round can coil, installation of the new system will (of course) be easy. If not, you'll have to modify your existing distributor/coil and find a place on your tractor to mount the new coil.

My bet is that Summit Racing is trying to sell you a round coil conversion which would be 3 ohms, no external resistor required because it's a ROUND coil. If you want to keep the front coil, a 12v front coil will be about 2 to 2.25 ohms and as Ed said , you will need the oem ballast resistor.

But........it's a Pertronix unit, so do as Jesse said.

Robert - The Pertronix 1247XT ignition system with a Flamethrower coil does not need an external resistor.

I can assure you that 3 Ohm coil will be fine, BUT the real answer is to use what the manufacturer says to use with their Ignitor, by contacting Pertronix.

I don't know anything about the Flamethrower coil, but I do know that if you use a standard 12-volt coil like you might get at Napa with a front-mount distributor engine, you do need to keep the factory ballast resistor installed.