farmall super m 12 volt conversion

archie3 · Apr 6, 2009

Hello all i just converted from 6 volts to 12 volts. is it absolutely necessary to have an idiot light in the wiring. i have a diode at the alt. and a ballast resistor at the coil. thanks Brad

Bob · Apr 6, 2009

If this is the typical Delco 10SI conversion you can use a diode OR and "idiot light" OR a resistor in the #1 "switched excite lead.

Note the "OR"... choose ONE of the three.

old · Apr 6, 2009

Once in a while you can get by with out the light or diode but not very often. Most on the time the alternator will back feed the ignition system and you will not be able to shut the engine down but some times you find an alternator that doesn't do it. I just did one on an M the other day and the alternator does not back feed
Hobby farm

Bob · Apr 6, 2009

WHY be proud of NOT using a diode (or one of the alternatives)... they are cheap insurance ($.05 to a couple of bucks) against alternator failure "down the road". If there is ever a poor connection or "open" in the charging circuit and there's no diode, resistor or idiot lamp in the "excite" circuit the alternator will charge it's guts out through the internal diode trio and voltage regulator letting all the smoke out of them.

<img src = "http://ndtc3500.stellarnet.com/~blweltin/Bob/DelcoSIA1A.gif">

<img src = "http://ndtc3500.stellarnet.com/~blweltin/Bob/DelcoSIB1A.gif">

John T · Apr 6, 2009

NO, Its NOT necessary to have an idio light if you already have a diode which prevents engine run on (via voltage backfeed to coil from alternator) when the ignition is turned off. The diodes work fine for that purpose. HOWEVER I actually prefer EITHER an idiot light ORRRRRRR a 10 to 47 ohm or so resistor even better for the additional safety current limiting they can provide PLUS they still prevent run on like a diode does...

This assumes a standard GM 10 SI three wire configuration youre talking about

Your tractor and your choice, either the diode or an idiot light or resistor work to prevent run on, you dont need more then one......

The purpose of the series external ignition ballast resistor is to drop the voltage and reduce the current when you use a 6 volt coil on a 12 volt system.

best wishes

John T

old · Apr 6, 2009

Very true Bob but all I am saying is once in a while you wire one up with out the light or diode and you can shut the engine down. Not saying it is good or bad not to put one in just saying it happens at time

Bob M · Apr 6, 2009

Actually many later GM cars equipped with the 10SI alternator had both idiot light AND resistor. The resistor was wired in parallel with the light so even if the bulb burned out the alternator would still work.

Bob · Apr 6, 2009

That's correct.

However, as I stated, any ONE of the 3 choices will work, and work equally well.

Bob · Apr 6, 2009

In other words, doing a half-assed job, when you KNOW better.

I'm the other way. I can't BEAR to have to tear into something 'cause it wasn't done right the first time. ESPECIALLY for a part costing CENTS!

JOSSETTE · Apr 6, 2009

ghj

archie3 · Apr 6, 2009

many thanks fellas, i used a hitachi alt. i just wanted to make sure. i had backfeed before i installed the diode and tractor would not shut down. now it shuts off with the diode. thanks again so much good help on this site.

69fastback393 · Apr 8, 2009

so if you use a light and later it blows the alternator will not work? so would it be best to use both?...thanks

farmall super m 12 volt conversion

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