140 won't charge/help John T

I have '78 140 with factory alternator that would not charge-shop amp meter shows none in addition to amp gage in tractor--installed new IH alternator and walla still no current on either amp meter. Also installed new fan belt and it is tight-no slippage. I am electrically ignorant so I need direction. It has 3 wire resistor next to alternator and I did not replace it. Don't know to check it.???

The originals were internal regulated alternators. With the appearance of an SI 10 connections. There is probably a fault in the exciter circuit. #2 terminal to the big terminal, #1 terminal to diode, or lamp, then to ignition. JimN

hmmm, can you repeat that in English? I am embarrassed to ask, but I said I was electrically challanged...

Is it a Delco alternator? Does it have (3) terminals - a large stud terminal marked "BAT" and a pair of small spade terminals marked "1" and "2"?

Post back and we'll go from there!

The caseIH parts explosion diagrams show the stock unit to be a side plug connected delco with internal regulator. Similar to or a SI 10.
Jim

Thanks for the alternator info Jim! (I'm not familiar with the 140 family...)

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Here's how to check the alternator on the tractor:

1 - Check resting voltage: Pull the aux (2 wire) connector from the alternator. With the ignition OFF you should see the following voltages to ground:
BAT - 12
Aux #1 - 0
Aux #2 - 12

2 - CCheck "key on" voltage: With the aux plug still removed, turn the ignition on but don't start the engine. You should see 12 volts at both Aux #1 and #2.

If you don't get the above STOP. Either the wiring is messed up or the alternator idiot light has burned out. It won't charge until the problem is found and fixed.

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If the above checks out plug the aux terminal back in. Now start the engine, run it up to full throttle for a moment then set throttle back to around 1/3 (1,000 RPM or so). Then:

3 - Take the voltage reading at the alternator BAT terminal. It should be 14 - 14.5 volts. If it's less the problem is the alternator.

4 - To determine whether the internal regulator is the problem, find the regulator shorting tab inside the "D" shaped hole on back of the alternator (photo). With the engine still running at about 1/3 take a small screwdriver touch the tip to the metal tab inside the hole. Now ground the screwdriver shank against the side of the hole. If the voltage jumps to 14 or more with the tab grounded it means the internal regulator is shot. However if still no change the alterator has other problems.

Good luck!

Wow, thanks fellas. This gives me a lot to work with and I think I can find my problem. I appreciate the detailed instructions--I know it's sometimes a hassle to type, but electrical problems are not my strong suit, and Bob you have given me something that I think I can understand and work with.