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MG MGA - coil ohm's

Guy's, Anybody know of the correct Ohm's needed for the 40K volt coils from Petronix systems. I am thinking of changing over the coil and points. They also refer to Non-ballasted systems or ballasted. What would be the difference?
WMR Bill

The real difference is whether the coil has the ballast resistor built-in or whether it expects you to use an external resistor or wire. Measure across the primary connection (the + and the -) with at least one side of the coil isolated from the vehicle's wiring harness. If you see about 3 ohms, it is internally ballasted and does not expect to see an external resistor. If you see about 1.5 ohms, it wants an external ballast resistor. With the harness still disconnected, turn the ignition on and measure the voltage from the hot side of the coil to earth. If you see full battery voltage (about 13VDC), there is no external ballast in the system. If you see 9 or 10 VDC, there is a ballast resistor in there somewhere (or your battery is low). IIRC, an MGA should be usning an internally-ballasted coil (3ohms). The pertronix coils are available both ways, so be sure to order the right one.
David "no MGA" Lieb
David Lieb

MGAs are not wired for ballasted coils so you should see your coil measuring 3ohms as David suggests. Then you should order the non ballasted high power coil.
Bob (robert) Midget Turbo

This thread was discussed on 16/06/2008

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