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Big resistor

F

fnofjr

Member
Can someone tell me what the large resistor in the Power supply wire to the coil is for on my ford 4000 tractor
 
(quoted from post at 13:16:25 08/10/17) Can someone tell me what the large resistor in the Power supply wire to the coil is for on my ford 4000 tractor
Click to expand...
would venture that someone replaced the factory resistance wire with your discrete resistor.
 
Normally, that would be a wire made of resistant material. He must have replaced it with copper wire and a separate resistor. When starting, a second wire that goes to the coil from the solenoid,
goes into use, which gives more power to the coil. Without resistance, the points would burn.
 
The wire is there because the coil was designed for 6 volts and the tractor has a 12 volt system. As to what it had originally that the others have been speculating on, that would depend on whether it is a 3 cylinder or 4 cylinder 4000.

The 3 cylinder 4000 came from the factory with a 12 volt electrical system and a 6 volt coil, and it had a resistance wire from the key switch to the coil to provide the voltage drop needed by the coil. If that original resistance wire went bad at some point, then a previous owner installed that resistor to replace the resistance wire that had gone bad.

The 4 cylinder gas engine 4000 was originally a 6 volt electrical system with a 6 volt coil. If it was converted to a 12 volt system at some point then whoever did that conversion installed the resistor to provide the voltage drop for the coil.

In either case, you could replace the coil with a true 12 volt coil and get rid of the resistor, but then you would no longer be able to utilize a bypass wire if it has one, which bypasses the resistor during starting to provide a hotter spark making it easier to start.
 
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