Electrical Problem

I had this on yesterday, but couldn't find it today. Converted a 420 JD Crawler to 12 volt. after just a few minutes of running, it starts to miss and will only run in an idle. A reply yesterday indicated it need a resistor in line, but didn't give the value of the resistor. Can anyone help?

Go to NAPA and tell them you want an ignition ballast resistor, it's a common part and they should be able to get it for you. It'll probably be a ceramic block with a tab on each end. Autozone part number is 150150.

A typical set up on a 12 volt tractor using a 6 volt coil would be for a series ignition ballast power resistor of around 1.2 to to under 2 ohms (Ive seen a lot of them 1.5 or 1.85 ohms)

John T

if this uses a regular can coil like is on a auto,youll be money ,time, and agravation ahead by simply walking into any parts store and telling them you want a 12 volt coil that uses no ignition resistor. if you dont want to go this route no one here can say unless we know the resistance of your existing coil,OR the new one you buy since yours is likely now bad. the idea is to simply limit the amp draw on your coil to a level it can handle without over heating. you typicaly will want a amp draw of around 3.5 amps or so on your ignition for long life and performance,so youll want a total ignition circuit resistance of around 4 ohms.this may be high a little but your alternator is putting out around 14.5 volts instead of 12. if you calculate it on straight 12 volts youll want a resistance of your total ignition circuit of @3.5ohms .so measure your coil(its MY opinion you should buy new as i believe once one overheats and tractor dies youve damaged it, but you could get by possibly) between the two small posts,find a external resistor to make your total resistance in ignition circuit between 3.5 and 4 ohms and you should be pretty close. as you can see, a coil that needs no resistor is far less complicated far less connections to go bad etc,but its your call .thats the theory behind the resistor anyway, i hope this helps!