Farmall 826 Electical issue.

[HydroTek]

1 hour ago, acem said:

Very possible an LED will not work.

The bulb acts as a resistor and provides voltage to initiate charging.

I don't think a LED will let enough voltage through to the regulator but I'm not sure.

My information above is based on my experience with 10SI alternators with internal regulator. The external regulator alternators may be different.

 

LED will work fine , and you are correct -- it will not pass enough current to excite the alternator

The resistor will provide the excite current path -- just need to be sure of the LED polarity , if you want to see it light 

[jim dog]

On 8/30/2026 at 12:19 AM, snoshoe said:

OK just to help you understand. Power comes from key switch to tell light. The blue wire carries that power from tell light to number 4 terminal on regulator. Power has to come back out F terminal of regulator. That will be the yellow wire and will go to F terminal of alternator. This is field current to start alternator. Once alternator starts half wave rectified half voltage current is available at the R terminal. That is carried by the brown wire back to the 2 terminal on regulator where it closes a relay inside and the light goes out. My suggested procedure; we know we have power to the light because it is on. We know it is grounded for the same reason. Check voltage at regulator terminal 4. No voltage wire is grounded between regulator and light. If you have voltage go to F terminal. No voltage grounded inside regulator. Have voltage go to F terminal of alternator. No voltage wire grounded between regulator and there. These test were done engine off key on. If you had voltage at the F terminal. Start engine you may have to rev it a little. Check voltage at R terminal should be half of what is on bat terminal. If not there is still a problem with alternator even if it is charging. If it is there. Then check voltage at terminal 2 on regulator. By now you should have the problem pinned down.

Before you start. I would have you check the regulator plug closely.  Make sure all 4 regulator terminals are straight and in line. Make sure both ends of the plug are fully seated and the plastic lock is locked. Lastly Make sure all 4 wires are fully seated in the plug.

Battery voltage not running  12.34 volts

F terminal at the regulator-4.72 volts

F terminal at the alternator- 4.70 volts

# 4 terminal at the regulator - 4.76 volts

Tested engine off key on

Snoshoe I wish I did have it pinned down.

 

 

[snoshoe]

44 minutes ago, jim dog said:

Battery voltage not running  12.34 volts

F terminal at the regulator-4.72 volts

F terminal at the alternator- 4.70 volts

# 4 terminal at the regulator - 4.76 volts

Tested engine off key on

Snoshoe I wish I did have it pinned down.

 

 

#2 at regulator

R terminal at alternator

Battery voltage all three while running

[jim dog]

On 9/6/2026 at 9:34 PM, snoshoe said:

#2 at regulator

R terminal at alternator

Battery voltage all three while running

Snoshoe I have some test voltage for you to look at.

Regulator, key on ,not running  # 4 terminal-4.45V  #3 12.21V  #2-.505v  letter -F 4.46v

Running  #4-4.30v  #3-12.28v #2 - 3.40v  letter F-4.30v

Alternator, key on  not running.

Battery-12.31v R-.549v F-4.49v 

Running,  Battery 12.32v R -.024  F- 5.25

I changed amp bulb tellite  from a led to a stander# 257  bulb and it did go out when running.

Do you think it should have been charging more?

[snoshoe]

4 hours ago, jim dog said:

Snoshoe I have some test voltage for you to look at.

Regulator, key on ,not running  # 4 terminal-4.45V  #3 12.21V  #2-.505v  letter -F 4.46v

Running  #4-4.30v  #3-12.28v #2 - 3.40v  letter F-4.30v

Alternator, key on  not running.

Battery-12.31v R-.549v F-4.49v 

Running,  Battery 12.32v R -.024  F- 5.25

I changed amp bulb tellite  from a led to a stander# 257  bulb and it did go out when running.

Do you think it should have been charging more?

Field voltage has been low all along. I have been attributing it to the extra resistance of the led. Normally expect it to be 8-10 volts how ever alternator should start with bulb removed and only resistor voltage available. Sadly if I ever had occasion to check what that voltage is. I do not remember. You had magnetism on the rotor bearing so we know there is current there. My thoughts are the rotor is shorted. Drawing all of the current available without producing enough magnetism to get the ball rolling. We know for sure you are not getting enough half wave voltage. I suspect when alternator was tested that they full fielded it and it probably worked fine for a while. That is about the best I can do without a personal inspection. My recommendation is to replace alternator or have it disassemble for a component check. Specifically the rotor and the R terminal connections.

This is no guarantee that regulator has not been damaged by high field current but at this time appears to be alright.

Would have been interested in the voltage with the 257 bulb

[snoshoe]

Jim right now I'm feeling like an idiot. You said with the 257 the light went out when running. Are the running voltages you posted with the led or the 257? If it was the 257 nothing has changed. If it was with the led. Then I need running voltage with the 257 at battery, R and F. If it is in fact charging then I need ohms of the resistor by the regulator. I think 10 ohms is correct. Wrong one could be causing this whole problem.

[acem]

IF we had pics working, the manual I posted in this thread would be helpful. It goes through all of this.

You can see the images if you Google redpowermagazine.com acem electrical manual.

[brahamfireman]

19 hours ago, snoshoe said:

Jim right now I'm feeling like an idiot. You said with the 257 the light went out when running. Are the running voltages you posted with the led or the 257? If it was the 257 nothing has changed. If it was with the led. Then I need running voltage with the 257 at battery, R and F. If it is in fact charging then I need ohms of the resistor by the regulator. I think 10 ohms is correct. Wrong one could be causing this whole problem.

The bulb won't matter on these, I know for a fact. All my tractors have a 257 blinking LED bulb in the oil and amp telelights.

My 856 has the 10DN alternator with external regulator and it works fine.

My 806 gas has generator with same external regulator. 

My 706 has been converted to a 10SI.

[HydroTek]

Generator = not the same regulator

but is similar looking 

Not sure 10 is the correct ohms for the alternator resistor 
-- I should have a couple in my toolbox -- next time I get over to the garage will check

would be the "red" resistor if the square type with screw terminals 
or the white if the flat type with spade terminals
-- there was also a white square one that had solder terminals 

white square type  with screw terminals was for the ignition coil 

[snoshoe]

2 hours ago, HydroTek said:

Generator = not the same regulator

but is similar looking 

Not sure 10 is the correct ohms for the alternator resistor 
-- I should have a couple in my toolbox -- next time I get over to the garage will check

would be the "red" resistor if the square type with screw terminals 
or the white if the flat type with spade terminals
-- there was also a white square one that had solder terminals 

white square type  with screw terminals was for the ignition coil 

Was thinking 10, 15 and 25. 10 was easy start 15 had to rev the engine to start and 25 was ignition. As Ace says I reserve the right to be wrong.

Well ai says I'm way off on ignition anyway.

[snoshoe]

2 hours ago, brahamfireman said:

The bulb won't matter on these, I know for a fact. All my tractors have a 257 blinking LED bulb in the oil and amp telelights.

My 856 has the 10DN alternator with external regulator and it works fine.

My 806 gas has generator with same external regulator. 

My 706 has been converted to a 10SI.

Bulb won't matter as long as resistor is correct. Wrong resistor and bulb can make all the difference.

[snoshoe]

Thinking on it I think they started the 10si with 15 then changed to 10.

[jim dog]

On 9/10/2026 at 7:50 PM, snoshoe said:

Thinking on it I think they started the 10si with 15 then changed to 10.

Snoshoe, I had a guy tell me the 4.5 " pully on it was to large he saId from the factory they were 2.5" or 3.00" So I put a 3.00" on it .The R terminal tested 6.14V F tested 4.35V  Battery at the alternator was 12.31V  running. I have not found any one yet that could test the armateur & field coils. As you seem to think my problem is the alternator which you could be right. I want to thank you for all your good  advice. I took her out on the road today first trip i was happy it run good handled well  even though i don't think it was charging.

[snoshoe]

6 minutes ago, jim dog said:

Snoshoe, I had a guy tell me the 4.5 " pully on it was to large he saId from the factory they were 2.5" or 3.00" So I put a 3.00" on it .The R terminal tested 6.14V F tested 4.35V  Battery at the alternator was 12.31V  running. I have not found any one yet that could test the armateur & field coils. As you seem to think my problem is the alternator which you could be right. I want to thank you for all your good  advice. I took her out on the road today first trip i was happy it run good handled well  even though i don't think it was charging.

Well it is not charging. Field voltage is to low. Since R voltage equals half battery voltage the alternator appears to be doing what it can with the field voltage it is being given. I would bet that a jumper from battery to F would really make it growl. It appears that relay in regulator is not closing. I would ask you to be sure regulator is grounded good. Path through regulator appears good since low voltage starts back at the bulb. Do you know if your regulator is mechanical or electronic?

[snoshoe]

I have assumed today's specs were with the 257 bulb. Was it lit, blinking or out?

[jim dog]

On 9/12/2026 at 6:51 PM, snoshoe said:

I have assumed today's specs were with the 257 bulb. Was it lit, blinking or out?

Yes it was the 257 bulb and i do believe it was out. How do I tell if the regulator is mechanical or electronic.I do know it's not made in the US. I'll double check the ground. if it's not running and i turn the switch on should the bulb be on ?

[snoshoe]

1 hour ago, jim dog said:

Yes it was the 257 bulb and i do believe it was out. How do I tell if the regulator is mechanical or electronic.I do know it's not made in the US. I'll double check the ground. if it's not running and i turn the switch on should the bulb be on ?

Yes bulb should be on with key on not running. If it is and goes out with engine running. That means relay is closing but current is not getting through regulator points. I can think of a couple or three reasons if mechanical. If electronic I believe replacement is the only way out. If cover is riveted on it will be electronic. If screws hold the cover on it could be either. Taking the cover off the electronic will just have a circuit board in there and alot of space. The mechanical will have a couple copper coils and two sets of points in there.