Help me with this electrical problem...

[frischtr]

I had a fusible link that was partially fused. If you moved the wire, the circuit would close. Move it a little more and it would open. Drove me crazy trying to diagnose why the tractor would shut down while in use, or start up on one day but not on another. Finally found it while checking resistance of all the components in the starting circuit. Was holding the link in my hand and it checked okay, then accidentally bent one of the wires and the meter read open.

I'm afraid that's what it may be... Trying to find something like that now.

 

[marrt]

Hmm. This is going to be a tough one.

Have you even seen an old incandescent light bulb with a broken filament that would still burn a while then go out when the filament heats up? The broken wires touch and make contact at first. Then, when the element heats up, the filament wires expand enough to break contact. It's possible a similar thing is happening here. The very small load of a continuity meter isn't enough to heat up and break the circuit. This is a guess of course. But this scenario fits your findings.

Or, perhaps a wire is abraded somewhere and shorts to ground under full load.

I'd go ahead and replace all fuses since it's easy and would be the most likely culprit for the "broken filament" scenario. After that, I'd make up a fairly long bypass wire the shielded alligator clips and start bypassing each wire, one by one, until I found the culprit.

Or, you could just wait until tomorrow and call Terry.

 

[MikeInEburg]

I think you'll find that's it's a safety switch causing your grief. Seat or PTO active or similar.

 

[frischtr]

I think you'll find that's it's a safety switch causing your grief. Seat or PTO active or similar.

No seat safety, and the PTO safety is not the issue (issue is still present after complete PTO switch bypass)

 

[frischtr]

Alright, got her running.

I went back and was checking continuity on all wiring while jiggling/bending all connectors, fuses, and terminals. I believe the culprit is the inline fuse holder between the starter and the wiring harness that leads to the front of the machine. I'm pretty sure i was having a loose connection there, so I took it apart. Looked good, put it back together and now everything works.

I couldn't replicate the connection issue there after pulling it out to where I could see it better, but I still suspect that's the issue. Going to get a replacement inline fuse holder and swap out the fuse. Fingers crossed, that is the issue.

At least now I can work on it in the garage instead of 100 yards away from my tools...

Thanks for the suggestions!

 

[Baby Grand]

Hmm. This is going to be a tough one.

Have you even seen an old incandescent light bulb with a broken filament that would still burn a while then go out when the filament heats up? The broken wires touch and make contact at first. Then, when the element heats up, the filament wires expand enough to break contact. It's possible a similar thing is happening here. The very small load of a continuity meter isn't enough to heat up and break the circuit. This is a guess of course. But this scenario fits your findings.

Or, perhaps a wire is abraded somewhere and shorts to ground under full load.

I'd go ahead and replace all fuses since it's easy and would be the most likely culprit for the "broken filament" scenario. After that, I'd make up a fairly long bypass wire the shielded alligator clips and start bypassing each wire, one by one, until I found the culprit.

Or, you could just wait until tomorrow and call Terry.

Yes - I've had that same experience with an incandescent bulb! Thought it was possessed.
Also had a 286 computer (remember those?) with a cracked circuit board.
When turned on, it would start up and by the time it was done booting, the board had heated up enough that it expanded & the crack opened, shutting it down. Absolutely, maddeningly, mystifying until I actually saw the crack in the board on the third or fourth tear-down.

frischtr,
Hope you nailed it!
Let us know if your diagnosis holds up after a few uses.

 

[frischtr]

Hopefully! I installed a new sealed, weather-rated inline fuse holder with a new fuse to replace the crappy clamp-on type. I'll be back to mowing shortly, so we'll see if it lasts...

 

[k0ua]

Well, I was going to try and help you, and I see you have it tracked down to a high resistance connection in the fuse holder. Ohm's law at work here. Just because you measure 12.6 volts in one of these circuits, does not mean it will deliver the current necessary to run all the things that need to operate on your tractor. A high resistance connection will still measure with a voltmeter the battery source voltage, but when you place a larger load on the circuit the voltage can drop to 0 due to the high resistance connection.

The hour meter likely only draws a few milliamps of current and was not enough to drop the voltage across the high resistance connection.

As an experiment to prove this to yourself, take a 1000 ohm resistor and put it in series with the battery and measure the voltage. You will find that the voltage measured thru the resistor is the battery voltage. Now take and put a load like a tail lamp in series with the resistor and to battery negative, and it will not light, and the voltage measured on the load side of the resistor will be near zero, and the voltage on the battery side of the resistor will be the battery voltage.

 

[k0ua]

Well, I was going to try and help you, and I see you have it tracked down to a high resistance connection in the fuse holder. Ohm's law at work here. Just because you measure 12.6 volts in one of these circuits, does not mean it will deliver the current necessary to run all the things that need to operate on your tractor. A high resistance connection will still measure with a voltmeter the battery source voltage, but when you place a larger load on the circuit the voltage can drop to 0 due to the high resistance connection.

The hour meter likely only draws a few milliamps of current and was not enough to drop the voltage across the high resistance connection.

As an experiment to prove this to yourself, take a 1000 ohm resistor and put it in series with the battery and measure the voltage. You will find that the voltage measured thru the resistor is the battery voltage. Now take and put a load like a tail lamp in series with the resistor and to battery negative, and it will not light, and the voltage measured on the load side of the resistor will be near zero, and the voltage on the battery side of the resistor will be the battery voltage.

To troubleshoot these types of problems. Place negative lead on battery post. Measure with positive lead along circuit path. You would have found the voltage drop across the fuse holder quickly by measuring one side and then the other side and noting the voltage drop with a load placed on the circuit.

 

[ponytug]

To follow up on K0ua's comments: having the load on is important. Put differently, you want to measure the current flowing, not just the voltage. You can pick up a good clamp meter on Amazon, or an OK one at HF. Woodland farms pointed to a good one awhile back.

Switches can look good by voltage until current flows, and then you discover that it actually had 100Ohms of resistance in it.
You can get copper loaded dielectric grease for coating relay sockets, and fuses. It keeps them from corroding and it keeps the connection at low resistivity. I use it all the time on boats, tractors, and english sports cars...:laughing: A little bit goes a long way.

All the best,

Peter