I have a 1975 IH Cub tractor that was originally 12 volt generator system. The previous owner converted that system over to 12 volt alternator. It wasn't showing ANY activity on the ammeter, and was discharging the battery over time, so I decided to take a look at it. When I removed the hood I saw that the ammeter wasn't even hooked up (no wires going to it). Everything else was, and when I stuck a screwdriver to the back of the alternator, it magnetized and proved to be working.

Here's where it gets weird....

I traced the original wiring (per the diagram), and the Gray & Red wires (gray coming from the alternator & red from the magnetic starting switch) were twisted and wired together back at the dashboard. I noticed from the diagram that both wires were supposed to hook to each of the terminals on the ammeter. I took alligator clips and cliped them to the ammeter, fired up the engine, and tested voltage at the battery. Multimeter started going nuts (voltage readings), and then I tested both terminals at the ammeter. Multimeter readings were going nuts.


WHATS THE PROBLEM!?

I was hoping to not go this far, but I am thinking a total overhaul of the wiring harness is in store. Just get rid of the old crap and put all new wiring in. Im just not looking forward to it because of the extra mess of wiring the magnetic switch, key switch and pushbutton.

Somewhere along the lines, the previous owner installed a push button start with a keyed on/off switch. The keyed switch is an ignition type, so maybe I can just make it a "key start".

If you guys have seen this problem before, and have a suggestion as to what is going on; maybe it will keep me from having to re-wire.

The ampmeter was bypassed because the alternator will peg the gauge. The alternator has a far higher output then the generator. The battery going dead may be a leaking diode in the alternator. What is voltage of the battery with the tractor running?

The most likely reason the amp meter was bypassed like that is due to the fact the alternator puts out a lot more amperage than the original amp meter was designed for. Gives you a direct connection from alternator to battery. I have wired several alternators over the years using original ammeter and got by most of the time. I just recently put a ammeter for a 66 series IH tractor in my own M to have a high capacity ammeter. It will charge just fine without an ammeter but you cannot tell what it is doing. Some install a voltmeter instead which works well. Only thing is , not many operators know how to interpret a volt meter reading. It will be showing 14 volts for example and everything is normal but operator thinks it is charging full blast when in reality it may be charging only a couple of amps as battery is full charge. On the other hand it cold be showing those same 14 volts and battery taking a moderate charge. When battery is low, voltage will be somewhat lower at same time heavy amperage may be flowing. Confused, well. You have to understand how a battery and electricity function to not be. But, in reality you don't really need to know all about it . Leave that for the mechanics. Just know what is acceptable normal readings. Far as replacing wiring, that is your call. If in tough shape I would.

I would have to hook the 2 wires back together to see, but when I check it with the 2 hooked to the ammeter, my multimeter went nuts showing numbers going up and down and all over the place rapidly. The ammeter never did move one bit during all of this, even no movement with key switch just in on position and tractor not running.

Digital multi-meters pick up a lot of hash whenever they are near an alternator. The voltage regulator in an alternator is a high frequency device which puts out many voltage waveforms which the leads on the multi-meter pick up. Use an analog meter to measure voltages when working around an alternator.

Well its funny that it started acting that way when I hooked both wire to the ammeter. Before when I checked voltages on the battery, it didn't act so crazy and gave a reading of 11.44.

I am thinking I just need to scrap the original wiring harness and re-do it with my own like I do the older Cubs. This one will just be more intense. I will also have to wire in a diode since its the alternator conversion. Maybe that will keep any current from the alternator from drawing. I did notice that the alternator was warm with just the battery hooked up.....although it is putting out when running, so its good there.

(quoted from post at 21:25:43 10/10/11) Well its funny that it started acting that way when I hooked both wire to the ammeter. Before when I checked voltages on the battery, it didn't act so crazy and gave a reading of 11.44.

.

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Brownie is correct about the digital picking up a lot of hash, but when hooked to the battery, the battery acts as an accumulator or dampener to knock down some of the trash frequencies.
I ruined a good digital meter when checking the output of my JD garden tractors stator. Should have known better as I was a maintenance technician for several years, plus 4 years working on radar in the AF. I thought I could read the output on the AC scale, but the high spikes must have knocked something out.

Well thanks for the info on that! I won't use my digital anymore on it.

At 11.44 volts the alternator was not charging.

If the capacitor in the alternator is bad it can cause a sensitive digital voltmeter to give widely varying readings. The regulator is either sending full field current through the rotor windings or no current through them. As a result the alternator output is either nothing or maximum voltage. The amount of time the field current is on compared to the time it is off is what determines the average output voltage. The capacitor in the alternator helps to even out the voltage output. Generally the higher the quality of the digital voltmeter the more times per second the voltage is checked and displayed on the screen which results in ever changing numbers. If your meter does not have some capacitance built in when checking voltage the numbers can always be changing. An analog meter simply can not react fast enough to these voltage changes and so the reading is steady. Simply adding a capacitor between the leads of your meter when checking the battery voltage with the alternator charging should make the results readable.

A simple cure for an ammeter that pegs out after converting to an alternator is to run a small wire between the two terminals on the back of the meter. It then becomes a shunted meter and will show amps based on the resistance ratio of the meter and the shunt wire. If you use a wire with the same resistance as the meter the amps shown on the meter will be half of the total amps flowing in the circuit.

Thanks for the good information Owen. When I stick a screwdriver to the round place in the middle of the alternator (toward steering wheel), it magnetizes. THis is done with the tractor running. Doesn't that mean that it is putting out?

My multimeter wasn't just going up and down in voltage and not staying put; it really was acting crazy giving me readings on the screen that just didn't make sense. There were some numbers, etc. It was moving FAST all over the place. That was when I hooked up the 2 wires to the ammeter like they should have been.

If yer alternator is putting out you should read 13.8 volts at the battery. No room for arguement here! So reading 11 something at the battery means the alternator isn't working. Now on a butcherd system that means that A. the alternator is bad or B. the wiring is bad.

You know you have wiring issues so fix that first! Then take the alternator in someplace that will bench test it.

Rick

(quoted from post at 19:56:41 10/10/11)

(quoted from post at 21:25:43 10/10/11) Well its funny that it started acting that way when I hooked both wire to the ammeter. Before when I checked voltages on the battery, it didn't act so crazy and gave a reading of 11.44.

.

Click to expand...

Brownie is correct about the digital picking up a lot of hash, but when hooked to the battery, the battery acts as an accumulator or dampener to knock down some of the trash frequencies.
I ruined a good digital meter when checking the output of my JD garden tractors stator. Should have known better as I was a maintenance technician for several years, plus 4 years working on radar in the AF. I thought I could read the output on the AC scale, but the high spikes must have knocked something out.

Click to expand...

There is something else there. Each side of the stator on your GT sould be putting out 28 volts AC at RPM's. I don't know how many I've tested with my digi meter and never had a problem. Oh wait! I know! It's that AF thing!!!!!! :twisted: :twisted: :twisted: Just teasing!

Rick (retired Army)

(quoted from post at 00:32:32 10/11/11) Thanks for the good information Owen. When I stick a screwdriver to the round place in the middle of the alternator (toward steering wheel), it magnetizes. THis is done with the tractor running. Doesn't that mean that it is putting out?

My multimeter wasn't just going up and down in voltage and not staying put; it really was acting crazy giving me readings on the screen that just didn't make sense. There were some numbers, etc. It was moving FAST all over the place. That was when I hooked up the 2 wires to the ammeter like they should have been.

Click to expand...

Having a magnetic field on the back of the alternator only means that the field coil in the rotor is being energized. You must have this magnetic field in order for the alternator to work but having the magnetic field does not mean the alternator must be working. The magnetic field is an alternator input, not an output. A problem with the stator or any of the diodes can reduce or eliminate any charging voltage output. A bad diode can also cause a poor output wave form or if it is shorted the alternator can output AC current. That could also cause your meter to go whacky.