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Hi, I'm new to the forum, I have a 1952 M37 which has been converted to civilian 12V ignition for a fire fighting truck. My question is about spark plugs, I have Champion J11C plugs in it, but when you look online there are always numbers that follow that J11C designation, can anyone tell me what those numbers should be ? Or is J11C the only numbers I need, thanks. BTW I am upgrading the distributor to a pertronix kit with a new 40,000 volt coil. Thanks for your help

Welcome aboard and congrats for saving another one! I'm not aware of any secondary numbers necessary for the plugs unless it's for the heat range-mine is also 12V and I run civvy plugs and wires. Just install a new set and gap them correctly. There are many vendors helping us keep them operational-several are forum members and freely offer their advice.
Gary

I just took one in with me to Autozone and had them cross reference it to 6 that would work for me.

its a good time switch to autolites. champions cant take the heat. centers melt right out of them.