806 D Alternator

My 4 wire alternator went out and I have a 1 wire to replace it with. What do I need to do to change the wiring to make the idiot lights work?

Thaks, Filo

You Cannot have a one wire system (not the best any way) and have an idiot light. Use a 10SI with the light placed in the wire going to the #1 terminal on the alt from the ignition coil 12v supply (before the ignition resistor) Jim

Filo -

You will be better off using a 3-wire Delco (10SI series) alternator. Will cost less, charge better at startup and is less likely to run down the battery if the tractor is not started for long periods. Also will properly operate your idiot light (a 1-wire alternator will not).

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Wire up the 10SI as follows:
- Large wire to the alternator BAT (output) post
- Relocate wire from the #4 terminal on the old VR to the #1 aux terminal on the new alternator.
- Connect a jumper from the new alt output post to the #2 aux terminal.

Cutoff/tape all other wiring at the (unused) VR plug.

(quoted from post at 12:58:29 06/17/13) Filo -

You will be better off using a 3-wire Delco (10SI series) alternator. Will cost less, charge better at startup and is less likely to run down the battery if the tractor is not started for long periods. Also will properly operate your idiot light (a 1-wire alternator will not).

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Wire up the 10SI as follows:
- Large wire to the alternator BAT (output) post
- Relocate wire from the #4 terminal on the old VR to the #1 aux terminal on the new alternator.
- Connect a jumper from the new alt output post to the #2 aux terminal.

Cutoff/tape all other wiring at the (unused) VR plug.

Click to expand...

This is what you currently have for wiring on your tractor.



The only problem you may encounter using Bob's solution is that if your light bulb fails the alternator will not start to charge. A resistor of equal or greater value than the light bulb connected between the #3 and #4 wires at the regulator will overcome this problem.

The #4 wire can be connected to the #1 or F terminal wire at the old regulator and then use that wire to connect to the #1 terminal on the alternator.

Bob is explaining how to wire up a 10SI 3 wire with internal regulator. For the dash light, I would use an LED with a 15 ohm resistor as a shunt across it to make it charge. Jim

If your "1 wire" alternator is a Delco SI type with the long rectangular regulator plug at the rear outer edge of the alternator case. (terminals set up like this[- -]. Then there is a good chance it will work with the charge light.

Go in the regulator compartment down in front of your feet, remove the old regulator and make a jumper wire with male blade connectors to jumper the regulator plug terminals at opposite(outermost) ends of the plug.
At the alternator, connect the "F" wire from the old square plug in the tractor harness, to the #1 regulator terminal in the new alternator, using an alternator harness repair plug from an auto parts store for any 74-84 GM product. Connect the small white(#1) plug wire to the harness "f" wire at the alternator. Also Connect the larger (#2) red in the new alternator plug to the "BAT" stud on the alternator rear using a ring terminal.

Thats it, the gen light should come on when you turn on the ignition and go off when the engine starts. The alternator is also now wired so any common 3 wire Delco SI alternator will work as intended if the "1 wire " alt ever fails and needs to be replaced.

I did this exact conversion to my 856 a couple years ago.

I should have added, connect the original heavy Bat wire in the original tractor harness, plus the red #2 wire from the new regulator plug, to the "BAT" stud at the rear of the new alternator.

My advice is assuming that you do have a Delco SI series "1 wire" alternator that uses the regulator plug shaped like this [- -].
Good luck, that SI series Delco alternator with the built in solid state regulator is much more reliable and has much better voltage control than the original Delco 10 DN with the external mechanical regulator.

Jim - Your solution will work too.

But presuming the OEM alternator is a 10 DN, the existing idiot light in the dash will work "as is" so long as it is wired as in my previous post.

Also - depending on the vintage of the tractor, a 15 ohm idiot light bypass resistor may already present in the form of a resistance wire in the dash harness.

Bob, I was not aware of any tractors using a resistance wire in the harness for the alternator. I know that it was used for alternators in Motor Truck applications but did not realize it was used in tractors also.

If your wiring harness is in good condition, there is no reason to cut it up to install a 10SI alternator.
When doing a rebuild of my 856, which included $500 of new wiring harness. I was not about to cut anything up to convert from the stock external regulator 10DN alternator to a 10 SI type.

I was able to simply adapt the wiring by removing the original external regulator( in the compartment down by your feet) and simply making a jumper wire to connect the outermost right and left regulator plug terminals.

To adapt the wiring at the new 10SI alternator, all that was necessary was to install an auto parts store harness repair plug designed for most any 74-84 GM product with 10 SI alternator. You attach a blade terminal to The white (#1)wire from the 10 SI alternator plug, and plug it into the F terminal of the tractors original harness alternator plug

Tape up this connection to protect it from weather or shorting. Connect the heavy red wire from the new alternators regulator plug using a ring terminal to attach it to the BAT stud on the alternator rear. This is all that needs to be done to adapt the original external regulators 10DN wiring to an internal regulator Delco 10 SI alternator. This will wire the tractor so the stock charge light will work with a ("1 wire") 10SI type alternator, or any standard 3 wire 10 SI alternator.
The original IH charge light works with no other changes.
The attached picture is of the several year old conversion done to my 856. The lump where the white wire enters the harness is the original harness alternator plug still atached. No need to cut up the original harness. It adapts easily to the 10SI type alternator.