??? on gm alt.

I have done these conversions for YEARS, and have settled on the particular diode shown, as it's ratings are WAY overkill, and it's still CHEAP.

Some folks use a diode of lesser current and reverse voltage rating, and claim they have good results.

HOWEVER, over the years, I had a few fail, and switched to the more robust 1N5408.

When the tractor is running, and the alternator is charging, there's no current through the diode.

When you turn the ignition switch "off", there can be a pretty good voltage spike from the ignition coil's primary, and that is what we are trying to protect against with the 3 Amp, 1000 PIV diode.

• Hobby farm

However I prefer the warning light over the diode for the simple reason people other than myself frequently run my tractors. And since most people ignore the ammeter, or they don't know how to interpret an abnormal ammeter reading I prefer the light.

Also an added bonus the light warns instantly should the fan belt break.

Thanks for the diagrams again! Once I (well, the Farmall Board) figgered out that a LED marker light doesn't pull enough current to get the alternator all excited I can plow snow after sunset. Now that is a mixed blessing.

I dont normally use the external diode in the excitation circuit (its just to prevent backfeeding the coil) but instead a 10 ohm current limiting protection resistor in its place and then in the event the engine would still run even with the ignition OFF I would add it. Unless the engine dont idle down very slow, with the current limiting protective resistor in place backfeed isnt usually a problem and you could even use an idiot light in its place which also provides current limiting protection.

It will work either way (diode or idiot light or resistor) and there doesnt seem to be any major problems with either the diosde or a resistor in my opinion. Its your tractor and your choice

best Wishes

Ol John T and all in Indiana