B1750 won’t start, mystery modules???

[PitViper]

The tractor has been running fine with no issues. Unloaded it from the trailer and parked it, now no power to the ignition switch. Battery has 12.1 volts, positive cable at the starter solenoid has 12.1 volts to ground. I did find two “modules” under the dash, one has four wires and has an arrow indicating which way it needs orientated up, it was just laying there unsecured. The other has three wires and no part number or identifying marks. The plastic housing is cracked. Can anybody tell me what these are? I have just the basic diagrams in the operators manual, but it’s not not real clear what these do.

 

[Dave_eng]

I have attached the no start trouble shooting section from the WSM.

Although you have measured voltage to ground, it would be prudent to remove the ground cable from where it is attached to the engine or frame and make certain the mating surfaces are clean and shiny.

Your model of tractor is different from most in that the engine is stopped by applying power to the solenoid on the injection pump for a few seconds.

For this system to work, there is a timer which, when you turn the key to OFF, applies power to the solenoid for a few seconds which cuts off the fuel supply for the few seconds it takes the engine to stop.

I have attached the page from the WSM which cautions about the orientation of the timer.

Since you report no power to the key switch, after checking the main ground, next you need to check the fusible link which will be at the starter. If you are not familiar with fusible links, think of them as a one time big fuse.

I do not know what the fusible link looks like on your tractor but I have included a photo from a B21. The fusible link is just a loop of special wire. The insulation is designed to resist the high temperature of the "fusible" wire melting under a short circuit condition. The link usually has a quick connector as part of its design to make replacement easy. Never replace a fusible link with ordinary wire. You could upgrade to a slow blow fuse if the link is burned out.

To test the link, you need to see 12 volts on both side of its connector.

The fusible link supplies almost every circuit of your tractor with power and must be verified.

Dave

 

[PitViper]

Thanks Dave. I think the “kill circuit” is dead. As long as I’ve owned the tractor, you could turn the key off and pull it out and the tractor would keep on chugging. Was instructed by previous owner to pull the fuel cut off to kill it. I’ll check the fusible link and see if anything is shorted out.

 

[PitViper]

Thanks Dave!!! Fusible link was burnt in two!

 

[Dave_eng]

Thanks Dave!!! Fusible link was burnt in two!

It takes a lot of current to burn it out so check for frayed wires or the like.

See attached for Messicks image and part #.

The Green colored wire signals a 40 amp fusible link.

Dave

 

[PitViper]

Oddly, my local dealer did not gouge the price too badly, it was under $8. I found a couple crimps that looked like they got hot and the insulators melted. After taping these up I traced the wires to the module with the directional arrow, so I am going to venture a guess that they are in the kill circuit. That said... I started the tractor, no issues... but I killed it like normal, turned off key switch and pulled fuel cut off knob to kill it, and a puff of smoke came from the starter area... burned the new link. I suspect the kill solenoid is shorting internally when it gets actuated by the manual fuel cut off. I am going to just remove it and try again tomorrow.

Thank you again for the help!

Edit: I did check the manual fuel kill linkage and confirm it was not interfering with/rubbing any wiring.

 

[Dave_eng]

Oddly, my local dealer did not gouge the price too badly, it was under $8. I found a couple crimps that looked like they got hot and the insulators melted. After taping these up I traced the wires to the module with the directional arrow, so I am going to venture a guess that they are in the kill circuit. That said... I started the tractor, no issues... but I killed it like normal, turned off key switch and pulled fuel cut off knob to kill it, and a puff of smoke came from the starter area... burned the new link. I suspect the kill solenoid is shorting internally when it gets actuated by the manual fuel cut off. I am going to just remove it and try again tomorrow.

Thank you again for the help!

Edit: I did check the manual fuel kill linkage and confirm it was not interfering with/rubbing any wiring.

You are making progress as seen by your smoke signals

I do not see how moving the stop solenoid manually could blow the link but who knows.

Since you are not using the solenoid, disconnect it then you will know if it is involved in the fusible link overload.

You turning the key to OFF and then stopping the engine manually. I am just wondering if, even though you are not seeing the engine stop, you are still exercising the stop solenoid timer/relay by your use and timing of the key. Leave the key on and stop the engine manually. This is just to rule out the solenoid. at some point you have to turn off the key and at that point the stop solenoid is energized even though the engine is stopped.

The fusible link protects circuits already protected by regular fuses. Check that the correct amp fuse is installed in each position and no one has bypassed the fuse by some trick.

As a temporary fix, you could splice an inline fuse holder into the fusible link and use inexpensive regular fuses until you get things debugged.

You only want to do this on a temporary basis.

Dave

 

[PitViper]

The fusible link protects circuits already protected by regular fuses.

I am sure this was true from the factory... keep in mind this tractor is about to have its 30th birthday lol. It has had a repaint at some point, every safety on it has been bypassed. When I got it the throttle lever was held together with a nail and it had a bungee cord holding the throttle lever in position and the keychain the key came on says 1750 will not move.

I really wish this thing could talk lol.

 

[PitViper]

Got everything sorted out. Timer relay was no good. It would supply power to the fuel shut off solenoid if you moved it. Confirmed earlier suspicion about solenoid shorting out. It was a perfect storm of two separate problems, and I’m guessing unloading from the trailer shook the timer relay just enough to give constant power to the solenoid.

Also figured out what the other mystery module was... blinker unit for the flashers.

Thanks again for the help Dave!

 

[Dave_eng]

Got everything sorted out. Timer relay was no good. It would supply power to the fuel shut off solenoid if you moved it. Confirmed earlier suspicion about solenoid shorting out. It was a perfect storm of two separate problems, and I’m guessing unloading from the trailer shook the timer relay just enough to give constant power to the solenoid.

Also figured out what the other mystery module was... blinker unit for the flashers.

Thanks again for the help Dave!

Enjoyed helping you and greatly appreciate your final chapter post which some fail to provide leaving all unwiser.

Dave