If it is 12V it needs a ballast resistor between the ignition lead and the coil or a coil with a built in resistor. 6V systems don't need them. Use a multimeter to test for 12V at ignition side of resistor and 7 or so at the other side. Test the resistance in both coil windings. There are lots of sites you can google for coil testing. Check your battery voltage and all grounds.
