Re: Farmall BN wiring

Posted by Janicholson on August 11, 2008 at 19:44:42 from (66.173.50.25):

In Reply to: Farmall BN wiring posted by BobPa. on August 11, 2008 at 18:40:58:

All though not exact in tail light details, A BN is the same as most Farmalls.
Your magneto needs to be left as is.
Do not rewire any part of it. The ignition Kill Switch on the box, is a grounding switch, and stops the engine by grounding the Mag when pushed in. It is an open switch when pulled out.

Reverse the leads on your existing AMP meter, or replace it with a higher amp rated one (50Amps is good) and make sure it is reversed from the original so it reads discharge with the lights on.

This means there will need to be a separate way to get power to the Alternator #1 terminal (small spade terminal in the housing) for exciting the unit into charging. I recommend a oil pressure switch that is normally open when no pressure is found, and closes at 3 to 5 PSI A NAPA item.

This switch will be placed in series with a lead from the Load side of the amp meter, (The pole of the Amp meter on the other side from the wire coming from the battery input from the heavy starter SW on the starter motor). From the Switch the wire can go to (either) an Idiot light using a turn marker bulb, or directly to the #1 terminal. The bulb will act just like a Fault light in a car, with no bulb, it will work fine, but no tell you if it fails to charge.
If you use a bulb, the bulb other wire is attached to the #1 terminal on the alt.

When the engine is not running, the system is not energized.

When it starts, the oil pressure closes the switch and voltage is sent to the #1 terminal (either through the bulb, or directly) and the alternator starts charging.

When the tractor is shut off, the pressure drops and the switch stops sending exciting volts, thus shutting of the system.

The #2 terminal should be attached to the big Terminal on the alternator. This is voltage control, and is needed.

I recommend putting a fuseable link rated at just over the alternator output (NAPA) into the #10 wire going from the Amp meter to the Starter Switch. This limits smoke if something shorts out. The heavy wire from the big terminal of the alternator should go to the Load side of the Amp gauge. Bob M diagrams will make sense of this. JimN

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