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Discussion Starter #1 (Edited)
Good Evening! I know there are several threads about battery discharge lights being on constantly, but after searching for a couple hours, I can't find my particular issue. I have a 1988 318 with the P218G motor. Suspecting the voltage regulator, I removed the clips from the two AC input wires. Measuring voltage across the two input wires, it is within spec, getting up to 50 at wide open throttle. Returning the two AC input wires and removing the DC clip from the center prong on the regulator, I am getting a little over 14 volts DC. This indicates a good regulator, I believe. However, once I return the DC wire back to the regulator, it measures only 12.05v when putting my multimeter back on the center prong. I remove the DC wire from the regulator and put my multimeter back on the center prong, and I get approximately 14v again. DC wire back on, I get 12.05v. For all of these measurements I am using the negative post on the battery for ground while the engine is running.

Measuring across the battery, I am getting 12.08v. Therefore, am I to assume its just measuring battery voltage when I have the DC wire on the center prong of the regulator? Is this indicative of possibly a bad ignition switch? Why am I only getting 12.05v DC on the regulator when the wire is on, but 14v DC when the wire is off?
 

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Have your battery load tested at an auto parts store. Most do it for free.I think you will find your battery is beginning to fail
 

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Discussion Starter #3
Have your battery load tested at an auto parts store. Most do it for free.I think you will find your battery is beginning to fail
Hi dhager! Thanks for the suggestion. I took battery to auto parts store. It was low (54%) charged, which makes sense as the battery light has been on for a couple months. Had them slow charge it back to full. They ran load test and it came back good.

Put battery back in tractor, same problem. When I run the engine at full throttle with the DC output line off the rectifier and test the DC output, it is 14-15VDC. As soon as I put the DC output wire back on, it gives me battery reading at any throttle position, including full throttle.

Any other ideas? Thank you in advance.
 

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Red,

This is exactly what you should expect to read as to voltage under the conditions you describe. When you connect the wire to the center terminal of the regulator, it goes directly to the battery + terminal through the 25 amp circuit breaker...see the diagram below:
318 charging circuit.JPG


Now that your battery is charged by the auto store, what is the terminal voltage? If the terminal voltage is more than about 12.7 volts, the lamp should not be lit on the dash, and will stay off untill the voltage goes below 12.3 volts -- see this theory of operation statement from the TM1590.
charge light for Onan engines.jpg


Chuck
 

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Discussion Starter #5
Red,

This is exactly what you should expect to read as to voltage under the conditions you describe. When you connect the wire to the center terminal of the regulator, it goes directly to the battery + terminal through the 25 amp circuit breaker...see the diagram below:
View attachment 259714

Now that your battery is charged by the auto store, what is the terminal voltage? If the terminal voltage is more than about 12.7 volts, the lamp should not be lit on the dash, and will stay off untill the voltage goes below 12.3 volts -- see this theory of operation statement from the TM1590.
View attachment 259717

Chuck
Hi Chuck! Thanks for the detailed response. I just fired up the tractor. I checked the voltage across the battery terminals and it was 12.58VDC and the battery discharge lamp was on.

Thanks!
 

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You need to check connections, most likely corrosion. Start at battery, then auto reset circuit breaker, key switch, VR, and finally the TDC module. Also check your grounds it is the 2nd item to check in the TM, with the battery being first.
 

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Being no help with this situation, I can only wonder why Deere decided to put all of this unnecessary electrical gadgetry into the 318. Today its even worse with the current models. None of this, the idiot lights, the time delay or the circuit board they decided to install bring any additional work functionality over the previous tractor models. Just problems. If I had a 318 that I needed for everyday work, (only tractor) I would eliminate all of it. This is one of the reasons I have no use for a 318.
 
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Chuck has provided the circuit diagram and Russ has wisely suggested checking connections at the various points. I would add one more suggestion. Your voltage reading precision indicates you are using a high impedance voltmeter which may be fooling you on the 14 volt reading on the regulator output. Is it possible to hook a load to that regulator ( I would suggest the headlights as the connector is right next to it), and then verify the 14+ volts at the regulator stays at 14 volts when power the headlights. Be careful with the test leads as the engine shroud can short things out.

I'm concerned that with only the voltmeter load, you could be reading a phantom voltage at the regulator output.
 

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Discussion Starter #9
Chuck has provided the circuit diagram and Russ has wisely suggested checking connections at the various points. I would add one more suggestion. Your voltage reading precision indicates you are using a high impedance voltmeter which may be fooling you on the 14 volt reading on the regulator output. Is it possible to hook a load to that regulator ( I would suggest the headlights as the connector is right next to it), and then verify the 14+ volts at the regulator stays at 14 volts when power the headlights. Be careful with the test leads as the engine shroud can short things out.

I'm concerned that with only the voltmeter load, you could be reading a phantom voltage at the regulator output.
Thanks dkarst! I will try that and look at the connections. When the tractor is running at full throttle, shouldn't I be getting ~14VDC across the battery terminals, similar to a car? If there is a problem between the regulator and battery, can I run some 10 gauge primary wire I have on hand from the regulator DC output directly to the battery? If I get ~14VDC at the battery at wide open throttle, that would confirm its not the regulator.
 

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Discussion Starter #10
Thanks dkarst! I will try that and look at the connections. When the tractor is running at full throttle, shouldn't I be getting ~14VDC across the battery terminals, similar to a car? If there is a problem between the regulator and battery, can I run some 10 gauge primary wire I have on hand from the regulator DC output directly to the battery? If I get ~14VDC at the battery at wide open throttle, that would confirm its not the regulator.
I think you might be on to something dkarst. I looked at all of the connections (e.g., circuit breaker, ignition switch, harness, etc.), everything looks good. I took the DC output line off the regulator again and confirmed I was getting over 14VDC out of the regulator at full throttle. I took some left over 10 gauge wire and connected the battery directly to the DC terminal on the regulator. At full throttle, was still getting only 12.6VDC across the battery terminals. I am thinking it is a bad regulator. I don't quite understand the concept of phantom voltage, but I eliminated all other connections and components by directly wiring the battery to the regulator. I will keep you posted.
 

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Leave the AC leads from stator on regulator. See whether the 14V you have at regulator will power a tail or headlight bulb. Measure if that 14V drops when regulator is powering that load.
 

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Discussion Starter #12
Did as you said. Made jumpers to the headlamp connector (I replaced mine with LEDs). Had the engine at idle, measured 12VDC on regulator DC output. Removed the DC output line, put my jumper to the headlamps, headlamps did nothing. Measured output, was getting nothing. Removed my headlamp jumper from the DC output and placed it on the + battery terminal, lights came on. Just as you thought, once I put a load on the regulator, I was getting nothing. Does that confirm that it is a bad regulator?
 

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I can't say 100%, but it sounds like a bad regulator.

Do you have or have access to a clamp-on ammeter? As well as voltage, the regulator also supplies amperage. Depending on the engine, 15 or 20 amps is minimum. Your voltmeter is telling you you have voltage, but you know nothing about the amperage...but thinking it's low. real low, and any load drops the voltage. Bob
 

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I think you're about there. I would like you to measure resistance from each stator lead to ground with engine NOT running to verify open.

For regulators, my poor memory is JD gets $90 for one, OnanParts.com has same thing for about $60, and you can get some aftermarket versions much cheaper but may have to fiddle with mounting. Check if you have a Cummins engine dealer near you as well. I'd also duplicate your measurement with a real incandescent bulb just for completeness and to show the LED headlights aren't fooling us.
 

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Discussion Starter #15
I think you're about there. I would like you to measure resistance from each stator lead to ground with engine NOT running to verify open.

For regulators, my poor memory is JD gets $90 for one, OnanParts.com has same thing for about $60, and you can get some aftermarket versions much cheaper but may have to fiddle with mounting. Check if you have a Cummins engine dealer near you as well. I'd also duplicate your measurement with a real incandescent bulb just for completeness and to show the LED headlights aren't fooling us.
Verified stator leads are open. I will see if I can find an incandescent bulb to run the test on as well. I will search around for the part. I am in Indiana, Cummins home state. Hopefully there is a dealer nearby. I will follow up and let you know if that is it. Thank you!
 

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Taillight will work but maybe you've swapped them for LEDs as well? Keep us informed of conclusions please.
 

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Whenever I've found a 300-series JD GT in my shop with really toasty wiring harness and a replacement from the dealer is too ridiculously priced, I just make my own simple wiring harness using the basic circuits. I respect engineers but some of the around-the-world, behind the gizmo in an unreachable spot engineering is just too much to bear. Not an approved solution I know, but simplicity is the best way IMHO.
 

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Whenever I've found a 300-series JD GT in my shop with really toasty wiring harness and a replacement from the dealer is too ridiculously priced, I just make my own simple wiring harness using the basic circuits. I respect engineers but some of the around-the-world, behind the gizmo in an unreachable spot engineering is just too much to bear. Not an approved solution I know, but simplicity is the best way IMHO.
Not only that, but I can build a much better harness than what came with the machine. And I really doubt these harness's are still available even if you are the type that requires 100% JD parts. But if you think the 318 was designed by Rube Goldberg, wait until you tackle a newer X series. It will certainly be interesting to see how many of these are around forty years from now. But it won't be me.
 
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I have several used, tested and known good, OEM 318 regulators, early and later style, 20A, in my spare parts bin. If you think one of these will work for you please pm me.
 

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Discussion Starter #20
Good evening all! Confirmed it was a bad regulator. Initially the regulator was testing okay as output was ~15VDC at full throttle. Tested the battery, and it came back okay. Looked at all connections and wires, they all looked good. On dkarst suggestion, I crafted a couple jumpers and hooked the headlights directly to the regulator output to put a small load on the regulator. It was putting out nothing, couldn't light even three LED headlamps. My multi-meter (and me) was fooled by phantom voltage. Put a known working regulator on it and problem solved, now getting ~14.5VDC terminal voltage with motor running. Battery light off.

I appreciate all of the recommendations/suggestions and education. Learned something from this experience.

Thank you!
 
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