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John Deere Tractors Discussion Board

Re: Wiring diagram for a 1951 B

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Posted by Clooney_shut down problem on January 02, 2004 at 09:49:37 from (

In Reply to: Wiring diagram for a 1951 B posted by JD-G on January 02, 2004 at 09:23:58:

JD-G, I'm pretty sure your [NO SHUT DOWN] problem is that you don't have a diode in the wire running from the tractor's ignition switch to the # 1 terminal on the alternator. At the very least you need a 10 ohm resistor in that wire.. If it still won't shut down then a diode will also be required.. If that circuit isn't protected from a back-feed from the alternator your coil will stay powered up from the alternator after the ign switch is turned off & the tractor won't shut down properly [or at all]..

~Read paragraph #7 & #8 in the below copy of my standard alternator installation directions..... Then read paragraph #2 on your ammeter reading backwards...... That should pretty well cover your problem..

~On the wire diagram you requested, send me your E-Mail address & I will send you the proper wire diagram showing your late "B" with a Delco distributor installed.. E-Mail me at

********How to correctly install a GM [internal regulated] Delco 10-SI alternator on a 2-Cylinder John Deere*********

~The Delco alternator you need will have the regulator terminals running like this [- -].........If the regulator terminals are running like this [.l l.], it is the old externally regulated Delcotron and won't work without an external regulator. The best Delco 10-SI alternators for tractor conversions are the lower output units with a 55 or lower amp output. Due to the high parasitic loads of the higher output Delco alternators at full charge they put a fairly high load on the early tractor's fan shaft drive gears.

(1)-First, the tractor must be, or have been, converted to 12 volt negative ground- [unless a high dollar positive ground, or expensive 6 volt converted alternator is used]......If the tractor is converted to negative ground, the ignition coil should have the [-] terminal hooked to the distributor and the [+] terminal hooked to the wire from the ignition switch. If the tractor is [or has been] converted from 6 to 12 volts and the original 6 volt ignition coil is used it will need an automotive ballast resistor [in series] installed in the wire running from the ignition switch to the ignition coil [+] terminal, [ the ''ECH 1CR13'' resistor from NAPA @1.82 ohms works good,, about $14.00 ]. If a 12 volt ignition coil is used it should be the internal resisted type. If in doubt about the coil type, or whether it has the correct resistance for a 12 volt system, just measure the coil primary resistance between the [+] & [ - ] terminals. If the resistance is over 3 ohms it is probably an internally resisted 12 volt coil & will function correctly at 12 volts without an added ballast resistor. If the resistance is under 2 ohms it will then require a ballast resistor between the ignition coil and ignition switch, or points burning will probably occur.

(2)- The wires should be swapped at the ammeter to reflect the new ground polarity [if the ammeter reads backwards when the conversion is done, the wires that are hooked to the ammeter are connected incorrectly and will need to be reversed]. Only one wire should be hooked to the battery side of the ammeter, that should be the wire running to the battery [non grounded side], or to the starter [battery cable stud]. All other electrical loads, including the wire from the alternator rear [BATTERY] stud should be hooked to the [NON] battery post of the ammeter. The exception would be a cigarette lighter, it would hook to the battery side of the ammeter.

(3)-The old generator & regulator should be removed, and [ if so equipped] remove the ignition switch and light switch power feed wire [L] wire that ran to the old regulator [L] terminal. The ignition switch and light switch feed wire(s) should then be hooked directly to the [NON] battery side of the ammeter, the old [L] wire going forward to the old regulator can then be eliminated...

(4)-The alternator should be mounted so the belt is tight and not out of line. If need be, the alternator 4 case securing bolts can be removed and case halves separated slightly [not more than a 1/4" or the internal brushes will fall out], then the rear case [with startor] turned so the regulator terminals are facing out and away from engine interference or exhaust heat.

(5)-A short 14 ga. wire should be made up and run from the big [BATTERY] stud on the back of the alternator to the #2 internal regulator terminal of the alternator. That is a low power battery sensing circuit so it doesn't have to be heavy gauge.

(6)-If the alternator is over 60 amps, a 10 gauge wire should be run from the [BATTERY] stud on the back of the alternator to the [NON] battery side of the ammeter. The old wire that ran from the ammeter to the battery [or from the ammeter to the big starter cable stud on the starter] should be replaced with a 10 gauge wire capable of handling the 60+ amps from the alternator. If the alternator is under 60 amps then the wires used can be 12 gauge.

(7)-If the tractor is distributor equipped, or has an ignition switch that supplies power to the coil/mag terminal instead of ground, a 14 or 16 gauge wire should be run from the coil power terminal on the ignition switch to the #1 terminal of the internal regulator. An inline 10 ohm [2 watt + ] resistor should be installed [in series] in that wire, [that resistor isn't required for the alternator to actually operate, but is put there to protect the diode trio inside the alternator from damage due to a power surge]. Make sure the resistor isn't taped inside the harness or placed close to anything that will burn as it gets quite hot when the ignition switch is on and the alternator isn't charging [I usually install the resistor at the ignition switch]. While a little over kill, the Radio Shack 10 ohm 10 watt p/n- 271-132 works very good and is under 2 dollars.

(8)- If the system charges, and the engine shuts off promptly when the ignition switch is turned off at high RPM, that's all you need to do. If the engine won't shut down consistently, or wants to run on a little after shutdown, or you just want to make sure it will always shut down correctly, then you can install a 1-2 amp 50 volt diode [in series] in the wire that is run from the ignition switch [coil terminal] to the alternator [#1] terminal. The diode is installed in series and in addition to the added 10 ohm resistor. The diode must be installed with the polarity indicating [stripe, dot, k, +, or cath,,,,, "cathode side"] towards the alternator and the [non] marked [anode] side towards the ignition switch. That diode is placed in the system to keep the alternator form back feeding the ignition coil when the ignition switch is shut off. Not all systems need that back feed protection [depends on the ignition coil] and once the alternator stops charging after shut down there is no additional power flow [from] the alternator #1terminal to the coil terminal on the ignition switch. I always include that diode in any conversion as it is easy and cheap and it won't have to be added later if a shut down problem arises. While again, a little over kill, the Radio Shack p/n 276-1141, 3 amp power rectifying diode will work good and is well under 2 dollars.

(9)- If the tractor has a magneto, or there isn't a functioning ignition switch, a 2 terminal oil pressure switch can be added to the engine oil pressure tap and a 14 or 16 gauge wire run from the big battery stud on the back of the alternator to one terminal of the oil pressure switch, then a 14 or 16 ga. wire run from the other oil pressure switch terminal to the #1 terminal of the internal regulator. Again, a 10 ohm 2 watt resistor should be added [in series] in that wire. A diode isn't required in this circuit due to no ignition coil interface.

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