12 Volt for Farmall C (Bob M)

I'm from Lakefield which is in the SW corner of the state by Windom and Jackson. Were are you from?

I didn't use any fuses.
Del

Keep in mind also if you select a warning lamp with a current rating TOO SMALL the alternator won't charge.

Problem is the current rating on the warning lamp is too great - it's backfeeding sufficient current to fire the coil after you shut off the ignition.

The solutions offered below are right on too. Either substitute a smaller lamp (like a #168 or #194 instrument/side marker bulb) or add a diode/resistor to limit the backflow current.

That being said, is there EITHER a 10 ohm current limiting protection resistor in your alternators excitation circuit from the coils high input side or the ignition switches output ORRRRR RRRRR RRRRR a 5 amp 50 PIV volt diode TO THE LIL SIDE NO. 1 ALTERNATOR TERMINAL?????

CUZ if not, when you trun off the ignition switch the alternator is back feeding the coil and keeping voltage to making her still run EVEN WHEN ITS SWITCHED OFF

I highly recommend a 10 ohm resistor in the circuit that excites the alternators lil side No. 1 terminal for protection. although she may be fine forever even without it, better safe then sorry I say. Thennnnn n if she still back feeds the coil and runs when shut off, simply add a 5 amp 50 PIV volt diode (one way current flow check valve) in series in the circuit after the voltage feed (coil or switch) and before the alternator to stop that run on problem. NOTE the diode MUST be wired + from feed and - to alternator so it can feed current into the alternator BUT NOT allow it to flow out of the alternator to feed the coil.

Sooooo oo, do you have a diode or a resistor in the alternators lil No. 1 excitation circuit????? ?? If not, therein lies the problem of why she runs even after shes turned off. The diode dont really need to be 5 amp rated, thats just what I use as its easier to wire.

See what Bob n the other good gents have to say.

John T