Coil resistor

Fri Apr 20, 2012 12:46 pm

My neighbor's 424 died, and had no spark. He replaced the coil, with no success. I changed the points and condenser, still no luck. We bypassed the coil resistor, and its running fine. 12 volt system, 12 volt coil, what is the purpose of the resistor, and can we eliminate it? Coil didn't heat up, with the resistor bypassed. Ed

Re: Coil resistor

Fri Apr 20, 2012 1:02 pm

It sounds like the original 6v coil was replaced with a 12v one . Since the tractor is 12v there is no need for a resistor to drop 12v to 6v.

Re: Coil resistor

Fri Apr 20, 2012 3:57 pm

DanR wrote:It sounds like the original 6v coil was replaced with a 12v one . Since the tractor is 12v there is no need for a resistor to drop 12v to 6v.

Thats what I thought, but wanted a second opinion. Thanks, Ed

Re: Coil resistor

Fri Apr 20, 2012 4:32 pm

Make sure the coil says 12 volts, internal resister. Many say 12 volts external resister. The ones that say external resister will run without it fr quite a while but will fail much sooner than with it.

Re: Coil resistor

Fri Apr 20, 2012 6:10 pm

I have always had the understanding that a resistor, whether internal or external, is necessary between coil and points to prevent points from burning. Start on full voltage and run on a lesser voltage.

Re: Coil resistor

Fri Apr 20, 2012 6:58 pm

To start on full voltage and run on lessor voltage you would need an extra lead from starter relay that bypasses the resister. a resister provides the same drop all the time.

Re: Coil resistor

Wed Aug 01, 2012 11:22 am

to add to what John said, a resister is needed in the circuit - either internally in the coil, or externally in the form of the big white resister. Automobiles in the 60's (12 volt) used a start circuit that connected 12 volts to the coil for starting, then went to the resister setup when you released the key to the run position. on Chrysler and IH vehicles that was done with the resister. on GM products, it was done with a resister wire to the coil. Fords i dont recall but i'm thinking resister.
if you burned out a resister, the engine would start and then die as you released the key. running for an extensive period of time with the resister bypassed will result in burnt points and coil overheating.

a 6 volt coil is just fine on 12 volts with the resister in place.