Alternator Conversion

Would one of the alternator conversion kits I see for sale for an M/SM work on my MD? I know the mounting brackets probably will not work but I cant think of any differences in wiring between the two other than not needing the ballast resistor as the MD is already 12V. What do you guys think??? Thanks for the help!!!

Matt - Here are a few options for alternator wiring:

---

1 - Presuming your MD has coil and distributor ignition (ie NOT a magneto!) connect the alternator's #1 aux terminal to the coil side of manifold switch. As soon as the engine starts on gas the alternator should begin charging. It will continue to charge after switching to diesel mode and the power to the ignition is cut off.

The downsides:
-If you use a warning light, it will be functional only when the engine's running in gas mode.
-If the engine spins to too slow on gas, the alternator MAY not begin charging. Solution is to swap in a smaller pulley onto the alternator.
-If you forget to flip the decompression lever back to the "run" position after shutdown it can drain the battery thru the alternator #1 terminal.

---

2 - Wire a simple momentary pushbutton switch between the battery + and the alternator #1 terminal. After starting the engine, push the button for an instant to start the alternator charging.

Downside here is remembering to push the button at startup.

---

3 - Install an oil pressure switch in the oil gage line. Then wire from the battery + to the pressure switch then to the alt #1 terminal.

You however must use a switch with a normally open contacts - ie. contacts that CLOSE when oil pressure is sensed. (This opposite from the standard oil pressure idiot light switch used in most cars.)

---

4 - Use a "single wire" alternator and dispense with the aux wiring entirely. I however don't recommend this for several reasons:
- One-wire alternators cost more than a standard 3-wire.
- Most 1-wires must be spun up quite fast to cause them to start charging. Your MD may not spin it fast enough.
- Some (not all...) one-wires suffer from excessive standby current draw. Thus an engine sitting unstarted can drain a fully-charged a battery in a matter of a couple weeks unless the battery ground cable is disconnected.

---

Hope this helps!

What Bob says about the speed problem is true. It can be hard to get enough RPM to start charging on a 1-wire. I'm going to change mine. It is a bit of a pain because the MD doesn't have an ignition switch as such. I use the touch method for now, but often forget to do it. It will start probably 50 times on a charge so you don't notice it until...

The existing lower bracket will not work but it is easy to make a replacement piece of U shaped metal out of some flat stock to fit the alternator. Drill 4 holes and away you go. I made the U a little long and shimmed the alternator to a good running position.

Tractor has a magneto and not a distributer. Not sure I understand why it matters if the tractor is running on gas or diesel for the alternator to charge in your one scenario. Dont see anything affecting the electrical regarding which fuel system is running.

I contacted the Brillman company and they do actually have wiring harnesses for MDs" with alternators. If I buy one of these to have a professional and somewhat original look, will I have to add extra switches, buttons, or lights? I have never done that on any of my other tractors. Thanks for the help!

Matt - The difference running on gas and diesel is the alternator needs a switched source of 12 volt power on the #1 terminal at startup to excite it so it begins to charge. Tapping 12 volts from the coil when the engine is running in gas mode (the only time there is an electrical "signal" available on the MD diesel) accomplishes this quite neatly.

Note one the engine is running in diesel mode, the ignition is killed. But the alternator will continue to charge from the initial excitation.

---

However since your MD has a mag, you are left with only options 2, 3 and 4.

For simplicity go with #2. But you gotta remember to push the excite button immediately after each start to flash the alternator. Otherwise after a few starts you will have a dead battery.

For reliability use #3. It's fully automatic and requires no action by the operator. (I have a buddy with a tractor wired up like this - it works great!)

Or go with #4 - but be aware of the possible drawbacks!

Ha well I feel dumb now. I really did know that...must have been having a lapse. Will see what happens I guess. All of my Farmalls are Delco 10SI alternators. Are those considered the "one wire"??? They have one wire post but also have a plastic plug with two wires in it. Thanks!

Well if they have a plug with 2 wires in addition to the large BAT wire then they are the standard "3 wire" 10SI alternators.

A one wire alternator will have a dummy plug (with no wiring) in the aux wiring connector port.