I am about to swap to Pertronix electronic ignition, it needs a minimum of 3 Ohms.  My car currently has a new GT40R coil but I cannot find the Ohm rating anywhere.  Does anyone have a clue as to the rating or do I need to buy one of the matching Pertronix coils?

Ignition coils with the R are used with a Ballast resistor (which is about 1.8 ohms) which then reduces coil input voltage to 9V. Coils without the R get the full 12 volts from the battery. Sounds like you need the non-R coil.

Cheers
Jamie

Typically they are 1.2-1.4 ohms

Cheers

Cheers, Pertronix sell a coil matched to their module, for about $59 I think I'll just get it that way the system works as it should, I was asking about the GT40R as I had bought it new and didn't want it to go to waste.

You can run gt40r with ballast(as per stock setup) and it will run perfect with Pertronix as it was designed as points drop in module and will run at 9v without any issues. If you want to run it at full system voltage you have to run appropriate resistance 12v coil such as recommended 3 ohm one.

R coil with ballast resistor/harness = 12v 3.0ohm coil

If you already have a new gt40r use it.
Cheers

With the Petronix kit you will have to have 12v ignition to the red wire don't put it on the coil if you still have a resistor inline they don't work to well . The Petronix coil will has a lot better output than a gt40 coil but if you already have one it will be fine

Cool, good advice.  There is no obvious resistor in line, I think Ford used different spec wire or something to reduce cranking voltage to the coil

gtv6capri
Cool, good advice.  There is no obvious resistor in line, I think Ford used different spec wire or something to reduce cranking voltage to the coil

Ford used resistive wire to drop voltage to the coil. While cranking however the resistive wire was bypassed and full battery voltage supplied to coil.

Cheers