yer right Mike, I was just thinking on the fact that the problem w/ full 12v to the coil is hot coil not burned points - the unresisted coils are designed to have that external resistance, the internal resisted ones work fine as I've had them on a number of 283's
internal resisted ones were/are used on these trucks when no external resistor is used - maybe the first 12v coils were actually 6v ones w/ the resistor added? the problem w/ too much voltage/heat on the coil is it damages the varnish on the winding wire over time
Bill