A GT40R is about a 6volt ciol.They put the resistor on them to drop the voltage,and there was another terminal on the starter motor to give it 12 volts when starting.The idea being that when cranking the voltage drops to below 12 volts (10-11) and a 6 volt ciol with 10 volts will give you a good spark when you most need it-starting.So on a 6 volt system a GT40R probobly won`t give you to many problems,don`t put a GT40 on it though,they are a 12 volt ciol.The R stands for resistor.
Hello Rod, We have used the older Massey 102 Senior with a 12 v battery and coil for a number of years. It had a basic cut out and high/low charge switch and 6v generator keeps bat up. It saves having a 6v battery. David.
Hi David. Sorry, but you lost me in your setup. Can you please explain in more detail. I've never heard of "basic cut out and high/low charge switch". Sounds interesting. My lights are still 6v, so would it blow the filaments?
Hello Rod, Our tractor is pre voltage regulators and did a lot of work in later years driving an electric welder. The only changes were the 12v battery and 12v coil, we had no lights but these would have to be 12v also. A cut out is a set of points on gen that close when charging to connect to battery. The charge switch sends full output to bat in high position and through a resister in low pos prevents overcharging . Presumably the higher voltage going to generator fields enabled it to handle 12v battery. Somebody with electrical know how could maybe comment if a 12 v regulator would handle it. On 12v the starter spins over and motor fires sooner. Regards David.