Farmall c conversion to 12 volt

I am converting my farmall C to 12 volts using the 10SI GM altenator. Al ot of the diagrams show using a warning light is it nessecary. Thanks in advance for your help.

The light is wired to the alternator in order to "excite" it so that it starts charging. It is not necessary under two conditions:

1. You are using a "one-wire" alternator.
2. The light is replaced with a diode in the circuit.

I just did a 12v conversion to a SC. an 'idiot light' is not needed.A new Delco one wire is 55 dollars with a 16 dollar core.The best way is to COMPLETELY strip out the old harness and rewire.Run one 10 or 12ga wire from alt to amp gage. Run the 'same' wire from the other side of gage to battery. Pull a 14ga wire from gage to ignition switch,then to coil. Done.Wrap the new 'harness' in a nice loom with black tape.Use a whole roll.Be sure to run a separate ground from alt to engine,dont rely on the mounts to ground.Sounds redundant,but seems to help.If you want lights,hook to amp gage to a light switch,then to lights.I use a push/pull type.I usually throw the old worn rotary away.You will probably need to install a 12v internally rested coil.However,I wouldn't till it is necessary.I've done probably 10 tractors as such.Mine and neighbors/friends. Never been a moments problem with any,ever.The first over 15 years ago.I don't know why everybody makes it so complicated with extra 'stuff'.

If your 10SI is configured as a so called "three wire" alternator it requires externally supplied initial excitation voltage (On its small side 1R terminal) and such can be accomplished in these ways:

1) Use a small incandescent (NOT LED) idiot charge indicator lamp which:
a) Provides adequate excitation voltage
b) Has sufficient resistance to prevent coil backfeed so tractor doesn't keep running with ignition OFF
c) Serves as an idiot charge indicator light (Off when adequate charging)

2) Use of a diode in the excitation circuit to supply excitation voltage PLUS prevents coil backfeed discussed above

3) Use of a 10 ohm resistor in the excitation circuit to supply voltage and prevent coil backfeed

4) Use of an incandescent lamp PLUS a resistor so it can still function even if lamp burns out

An incandescent charge indicator lamp is a good plan as it accomplishes more then one task and more then a resistor or diode alone can provide, and its cheap n easy.

Maybe the other gents have yet more ways to excite the Delco 10SI Three Wire but an idiot light is still a good multi functional system

ANY OF THE FOUR WILL WORK

John T

Right on John T!!

I prefer a warning light myself - especially if others are going to be running your tractor. In addition to indicating if the battery is not being charged, it also instantly warns if the fan belt breaks.

I think we agreed on that years ago lol You long ago mentioned an added resistor in case the bulb burned out !!! I forget if the small 12 volt indicator lamp is a 194 or what??

John T

#194 indeed John - you have a good memory! A #168 dash indicator/side marker lamp also works.