Weekend Freedom Machines banner
1 - 20 of 47 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter · #1 ·
A few weeks ago, my 318 battery indicator light would flicker about an hour into mowing. Found a loose headlight wire, assumed that was the cause. Next time out, same problem - but after flickering for 5 minutes or so, it stayed on and then blew the 3A fuse. Fuse appeared to be original and was so degraded I had to replace the in-line fuse holder. Now, the machine fires and runs fine, but battery light stays on. As soon as I engage the PTO, the blades run for 1-2 seconds, then blows the same 3A fuse. Found a mildly exposed/broken section on the 2-wire PTO harness, replaced that as well as the PTO switch with OEM parts. Still has the same problem. However, if the coil is unplugged, the battery indicator stays on but the fuse does NOT blow when flipping the PTO switch. I get the same result with the engine either running or off. Coil plugged in, fuse blows. Coil unplugged, fuse doesn't blow - but the battery light remains on either way. Searching other WFMachine threads I find this circuit only goes to the seat switch and TCDM - and it's typically a seat switch issue. I did in fact find a loose wire at the switch that I have since reconnected - but the problem persists. If the coil has a short (my current theory), why is the battery indicator still lit up even with the coil unplugged or disengaged? Fender deck and battery tray are both still out and I have looked for any bare or broken wires along every inch that isn't sheathed in the harness - found none and couldn't elicit a reaction by messing with any of the length of harness or connections that might be suspect, including the newly crimped in-line fuse. I'm a mildly (but not overly) intelligent human, just a poor mechanic. Any suggestions from the group?
 

·
Registered
Joined
·
57 Posts
Consider the possibility of having two separate issues. I would start with cleaning the battery connections and checking resistance of the PTO coil. I do not recall what is normal resistance but it is easily found via google. If the coil has two wires make sure the ground side has a good connection. Oh and of course, first and foremost, check all grounds.
Provide us with feedback on your findings, there are procedures to check the charging circuit starting with AC output from the stator then DC output from the regulator/rectifier.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #3 ·
Thanks for the help. Answers to your questions: Battery/cable connections are new and clean (new battery and cables all new in the last few months). However, I've also had the battery out to access the wiring underneath the tray and the same symptoms persist when using a jumpbox to start the machine. I tested battery output initially but, I guess it's possible that I've burned enough voltage in testing to fall below the amount needed for the charge light to go off after replacing the worn harness... I hadn't pondered that before. I forgot to mention that my multimeter shows 0 ohms on the coil, which would appear to indicate a short. The PTO does still engage however, both with the switch (before blowing the fuse) and when hotwired with my jumpbox when I checked it separately. I have a replacement on the way, but can't seem to explain the persistence of the battery indicator with the PTO unplugged? I have checked all grounds and the only loose one I find is a stray cable behind the dash - from the hour meter perhaps? I can't remember exactly off-hand, but this appears to be typical gauging from previous WFM discussions and the wiring diagram. I will try to re-check the grounds again today to see if I've missed anything.

Thanks again for the help so far. Assuming I haven't missed any grounds... other thoughts?
 

·
Registered
Joined
·
1,555 Posts
I’d charge the battery fully and then run it. The light works well and is sensitive. If it’s a tiny bit low the light will come on. I have an extra set of battery cables I can piggy back to my cables so I can hook up the battery on the floor and run the tractor to do diagnostics.
 

·
Registered
Joined
·
302 Posts
I'd suggest to test the voltage regulator, to make sure the battery is charging min voltage or 12.7 and max 13.8 volts.
 
  • Like
Reactions: fuddyduddy

·
Registered
1989 318
Joined
·
2,670 Posts
The article I always reference says 12.9 - 14.1, anything less than 12.9 will not charge the battery.
 
  • Like
Reactions: fuddyduddy

·
Premium Member
Joined
·
9,686 Posts
A front PTO winding in good health will have a DC resistance of 3.4 to 4.9 ohms. If the PTO on your tractor has an internal short, it would blow the 20 amp fuse, or trip the 25 amp circuit breaker.

For a 3 amp fuse to blow immediately, you are correct in looking at the seat switch and its harness. Here is an excerpt of some of the wiring details:
Product Schematic Font Rectangle Slope


F1 is the 20 amp fuse, and F2 will be a 3 amp or 2 amp fuse depending on year model.
Musical instrument Guitar accessory String instrument accessory Music Font


As mentioned by other members above, the dash battery light indicates the voltage of the system and NOT the charge state...see this manual excerpt:
Font Terrestrial plant Rectangle Circle Screenshot


Notice that the battery charge indicator lamp is driven by the TDCM which gets the battery voltage state from the F2 fuse at connector X23 pin 5 (the same place the seat switch voltage is sourced...) If you are having issues with the fuse blowing, the battery light staying on, etc. then concentrate you attention in this area. It could be an intermittent or partial short to frame of the seat switch harness which is routed below the fender pan. Inspect this area of the harness for any damage. Let us know what you find...

Chuck
 

·
Premium Member
Joined
·
9,686 Posts
One more thought -- if the battery light is on and that is the only remaining symptom, perhaps the charge system is not working up to par... Check the output of the stator (this is an AC voltage...) and then the regulator output to the battery . The tests are in the TM1590.

Font Parallel Screenshot Document Paper product


Also check for the stator being isolated from engine ground, as a short here can adversely impact charging performance...
Rectangle Font Parallel Slope Number


Chuck
 

·
Registered
Joined
·
109 Posts
Suggest taking the ignition switch connections off, checking connections and fully seating back on the switch. I had multiple issues that were fixed by re-seating the connections. Comon problem as the spade connectors' seating in the plastic harness deteriorates over time and corrosion can take place, resulting in poor electrical connections. Since almost everything in the tractor runs through that switch, it's crucial for it to be in good repair.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #10 ·
Update:

I've had the fender deck off for a few days and have scoured everything visible on the seat switch and harness. The switch is currently jumped, but I've both hooked up the original seat switch and reseated and secured the jump wire and neither have any effect. I can't find anything that would result in a short - unless it is inside the harness insulation and not visible. That said, I see nowhere on the harness insulation that resembles having been pinched or in a bind that might have caused an internal broken wire... I've even fiddled with the seat wiring to see if I can get any kind of response on the battery lamp, but no such luck. Cruisin' mentioned the ignition but I've also replaced that as well in this process and all connections are secure. I've adjusted and cleaned up some things here and there but always with the same result. PTO engages for about 1 second, then blows the 3A fuse. If the only pathways in this circuit are to the seat switch and the time delay, should I be concerned that the TDCM is the issue?

Thanks again for everyone's help so far. Still at a loss on this one though...
 

·
Premium Member
Joined
·
9,686 Posts
DCT,

There must be a shunt circuit somewhere that is blowing the 3 amp fuse, as the only loads on that circuit is the seat switch and the pin 5 of X23 on the TDCM which is the input to he battery charge voltage detector IC internal to the module itself. Are you sure that you don't have the two fuse values reversed in the holders/sockets? You mentioned in the first post to this thread that the "in-line fuse holder" was in bad shape and you replaced it -- that implies that your tractor is an early model below SN 475,000 and would have had a 2 amp fuse in the F2 location. Try physically tracing the wire routing and colors at the fused to verify the harness is wired as it left the factory.

One more thing to try -- if the fuse blows after one second of PTO engagement/switch actuation, does this happen even if the PTO itself is not plugged into the harness? You may have noticed that there is not supposed to be any harness interconnection from the 3 amp fuse to the PTO wiring at any point in the factory configuration. If you do not actuate the PTO, does the 3 amp fuse ever blow?

Is the dash battery charge lamp still flickering or staying lit? When this occurs, what is the voltage at the battery?

Once we find the root cause of your symptom, it will all make sense, so thanks for hanging in there...

Chuck
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #12 ·
Chuck,

I agree - something's not quite adding up but once the problem comes to light, hopefully this will all make sense. I appreciate you folks bearing with me and my lack of electrical proficiency. Answers to your questions:

- I agree it seems like there should be a short somewhere in that circuit, I just can't find one. That doesn't mean there's not one there... but, if there is, I just can't seem to find it.

- Yes, I had to splice in a new in-line housing but the wire colors all match up to original factory specs, so I'm sure the correct fuse is in the correct place. From my reading, I knew some were 2A and some were 3A. I initially used a 2A fuse which blew as soon as I turned the key. I assumed it needed a 3A fuse instead, which is what I'm running in it now. However, perhaps it's supposed to run on a 2A fuse and that's just another symptom? Yes, it's an earlier model: 426,xxx.

- Yes, the fuse pops about a second after flipping the PTO switch. This is true both when the engine is running and when it's off but the key is on. If I disconnect the PTO coil, I can flip the PTO switch (and the PTO light comes on) but the fuse doesn't blow. Again, this is true whether the engine is running or off. If I don't engage the PTO, the fuse is fine. Again, same result with engine running and off, and with the coil connected and disconnected.

- Dash battery lamp only flickered before the initial fuse blew while mowing. Ever since, it's been staying lit. The battery and tray are pulled out at the moment, so I'm either running the mower with some fairly long jumper cables, or my jump box. My cheap, analog multi-meter showed something between 12-13 volts earlier today while the mower was running and the light was on. However, I'm not sure if the added resistance of the long (and somewhat cheap) jumper cables would cause a lesser reading from the charging system. It's also possible that the battery is slightly low as I've been using it to test things out, but not really giving it time to charge in the system or putting it on charge overnight... That said, it is fairly new as I just replaced it in March.

Lastly, I did find another thread with a similar issue on another 318 - blowing the 3A fuse when engaging the PTO. In his case, he eventually replaced the whole PTO clutch/coil which seemed to solve his problem. Although I understand that shouldn't be the case... I'm wondering if, for some odd reason, that might be a possibility? That thread is here: 318 PTO blows 3A fuse When testing resistance on the coil, I get a reading of 0 ohms. But, if it's really that far gone... would it even still engage to begin with? And, that still wouldn't explain the battery indicator when the coil is unplugged?

Thank you again. I appreciate both your help and your patience!
 

·
Registered
Joined
·
690 Posts
Your short may be at the tail end of the PTO coil, were you have current going through the coil enough to activate it, but yet also having a short in the system giving you the 0 ohms.
 

·
Super Moderator
Joined
·
4,358 Posts
Your short may be at the tail end of the PTO coil
But wouldn't it give a ohm reading through the part of the coil it passes through? I understand it would be less than the 3.8 to 5.0 of a good coil. And with a lower ohm reading doesn't it require more amps to get the coil to engage?
Just some thoughts as I am not an electrical expert.
 

·
Registered
Joined
·
690 Posts
But wouldn't it give a ohm reading through the part of the coil it passes through? I understand it would be less than the 3.8 to 5.0 of a good coil. And with a lower ohm reading doesn't it require more amps to get the coil to engage?
Just some thoughts as I am not an electrical expert.
More amps will cause the fuse to blow, and if he has a dead short at the tail end of the coil, the current still goes through the coil till it finds the short. Put a dead short anywhere in 100 ft of wire and it will probably still ohm out at 0.
 

·
Premium Member
Joined
·
9,686 Posts
Jake,

If the short is internal to the coil, the resistance will be lower but not zero unless the short is right at the beginning. A low resistance PTO coil such as 1 to 1.5 ohms will still activate the PTO, but may get hot and may blow the 20 amp fuse or trip the 25 amp breaker (as the PTO current adds to all the other normal loads of the tractor.) The mystery here is that the F2 fuse is blowing, not the F1 fuse -- the 3 or 2 amp fuse does not power the PT) coil...its power comes through the TDCM from the 20 amp fuse.

A 3.5 ohm PTO by itself will draw about 3.7 amps when the battery is being charged at 13 volts. A 4.9 ohm coil will draw only 2.65 amps under those same conditions -- but this is still enough to blow a 2 amp fuse and it is easy to see why the PTO is not powered by the F2 fuse in these tractors. When the PTO coil fails enough to have only 1.5 ohms of resistance it will draw 10.6 amps by itself and when combined with other loads such as the rear PTO when fitted, the headlights, and the ignition can easily blow even a 20 amp fuse.

DTC says he is still having a charge lamp showing, and is running the tractor from a "jump box" which might also be a battery charger. Units like these often have a large ripple content to their output, and while the average voltage may be 13 volts, there are large variations instantaneously. I would like to know how the charge lamp acts with a fully charged 12 volt battery in place as it normally would be.

Try unplugging the TDCM X23 connector and then removing/masking off just the Pin #5 to isolate it from the module when you plug it back in. This will cause the charge lamp to always be lit, but isolates the 3 amp fuse wiring from everything except the seat switch circuit. The PTO should still activate, and we will see if the fuse blows...

Chuck
 

·
Registered
Joined
·
66 Posts
I'm a retired electronic technician of 43 years, so I know that & keep our equipment going but don't claim to be a mower mechanic. This may be helpful or not. The PTO coil is apparently an electromagnet, two leads so when energized engages. Coil winding resistance of 3.8 to 5 ohms which is roughly 3-4 amps (ohms law). As chuckv pointed out that's protected by 20A fuse, 25A breaker. The coil should be insulated from ground, insulated from the PTO metal coil housing which touches ground by chain (mowers I have).
Troubleshooting blown fuse it's better to temporarily sub in the same amperage circuit breaker. Otherwise you go through 100 fuses trying to find the problem.
By moving wires, etc, breaker trips...much easier finding the problem.

Sent from my SM-S205DL using Tapatalk
 

·
Premium Member
Joined
·
9,686 Posts
DTC,

I'm still think about your issues and have yet to come up with any reasons for a 20 amp circuit load to blow the 3 amp circuit fuse. The only place any of these two paths get close to each other is in the TDCM and the X23 connector. You might as well inspect that connector for any signs of arcing or conductive contamination. The 20 amp connection from F1 is on the pin 3 of X23, and the 3 amp connection from F2 for monitoring battery voltage is on pin 5. I did work up a document some time ago where all the TDCM connections, functions and normal conditions were enumerated, so it might help:

Font Parallel Paper Document Paper product

When the battery charge light on the dash is light, what is the exact voltage you read on Pin 5 of X23? Also, what voltage do you measure on the pin 9 of X22 with the seat occupied or the seat switch jumped? Borrow a quality meter if you don't have one, since fractions of a volt are meaningful here...

Chuck

Minor errors in pin numbers were corrected in first paragraph text above during recent edit -- 6-21-2022 at 1:46 MDT.
 

·
Registered
1989 318
Joined
·
2,670 Posts
I am wondering if his wiring has been butchered and things are not connected as the schematic shows??
 

·
Premium Member
Joined
·
9,686 Posts
Tom and DCT,

There may be hacks (or failures) in the harness that we have yet to discover... I still can't understand why unplugging the PTO from the harness allows the F2 (3 amp) fuse to remain intact when the PTO function is enabled, yet it gets blown if the PTO is plugged back in under those same conditions. There should be no connection between the two functions.

There may be something failing inside the TDCM -- so lets look at how the internals of that module work. I don't have the exact detail of the internal wiring of this module...just the functional equivalent diagram that Deere provides in the manual, as shown below:
Product Font Schematic Rectangle Parallel


The 3 amp fuse (F2) connects directly to the X23 pin 5 via the #500 red wire, then continues on through the seat switch and harness to the X22 pin 9 via the #810 pink wire. These are the only two loads on the F2 fuse, so lets look at what they do once they enter the TDCM.

Pin 5 of connector X23 connects internally to the Battery Discharge Lamp Control block in the TDCM. This block has only two other connections shown, the ground connection on the right side going to X22 pin 10, and the lamp drive connection on the upper left side that goes to X23 pin 1. There might be some components inside this Lamp Control block that draws excessive current from the F2 source -- but it is hard to conceive of what that might be that would be conditional on the PTO coil being connected.

The other load for the F2 circuitry is the X22 pin 9 where the seat switch connects to the Time Delay integrated circuit. That block has a single output connection which goes to the base of transistor B. When transistor B is conducting, it provides a ground connection to relay G and through the diode C to the other relay which enables the ignition when its contacts are closed (connecting the X23 pin 3 -- the 20 amp fuse supply input, to the X23 pin 2 -- the ignition coil and the hour meter.) Relay G is the control for the PTO source voltage, connecting the 20 amp source at X23 pin 5 to X23 pin 4 when closed and providing a voltage source to the front PTO switch at X4 on the #760 blue wire.

The power to the relay G coil comes from either the safety switch path when both PTO switches are OFF via diode E, or once the relay contacts D are latched on, through the connection to the other relay and the X23 pin 3 input from the 20 amp fuse.

Since we cannot know for sure what is inside the two blocks labeled Time Delay IC and Battery Discharge Lamp Control, it is hard to envision what component failures might be at play here that could cause the symptom detailed in this thread.

Swapping out the TDCM for a known good unit would perhaps be helpful, but harness hacks can be a source of causing module failure, and it might be risky to do such a substitution. Certainly you would not want to simply start an expensive parts replacement activity here, as these modules are not returnable to the dealer and now cost about $490 each. :eek:

Chuck
 
1 - 20 of 47 Posts
Top