M920 - starter spins but does not engage upon connecting batteries

[farmer73]

...long post...lots of details...50 yr old rookie here...

As I was connecting the batteries on my M920 today, it sounded like the starter began spinning even though the ignition was off and the key was not even in the truck. It was only spinning and not engaging. It was a constant humming noise; no clicking or anything else. I had to disconnect the batteries to stop it (and was not even done hooking them all up). As soon as the back 24V bank was connected and the main positive cable to the starter was connected, it the spinning noise began.

Questions:

1. Does this mean the ignition switch is bad? Where can I get a new Pollak ignition switch? Will John Deere ch11696 also work per https://docs.google.com/spreadsheets/d/1hmbUQuMi5MmXIomIh82J5lc8vKp0RvZ4qcz7zcwPMYc/edit?pli=1#gid=0
2. Should I also replace the starter relay with: John Deere Starter Relay RE170320?
   1. Is the starter relay the thing to test/swap first here?
3. Is it possible the Starter Solenoid is also bad now too?
4. Is the M920 supposed to have a positive-ground or a negative-ground electrical system?

When I started the truck the other night, it stalled after about 20 seconds. When I attempted to restart by pressing the start button, it sounded like the starter began spinning but not engaging (even after turning the ignition key off, it stayed spinning), and it sounded like the air compressor was also still running. I had to disconnect the batteries to stop both noises. When I disconnected the main negative cable at the battery bank, the compressor (louder noise) stopped. Then when I disconnected the main 24 volt positive cable, the humming/spinning noise stopped (I think this was the starter). However, I think the low pressure air alarms turned off when I turned the key off before jumping out to disconnect batteries, so that makes me think the starter relay and/or Starter Solenoid are bad.

A few days before that stall, the truck started and ran for about 20 seconds before stalling. That time, The start button did not trigger any response when attempting to restart after the stall. I disconnected all batteries and found that the right side of the battery bank had both batteries down to 10.7 volts and they would not take a charge from an automatic charger. I tried using a recondition feature on another battery charger, but after days of running this cycle in 24 hour intervals, I bought 2 new 6TL batteries instead so I could move forward more quickly. All 4 6TL batteries were less than 2 years old and get disconnected between truck uses. I always test each battery before connecting them and they were all at 12.9v.

After that stall where the 2 right side batteries were impacted, I began checking all wiring (while learning it all). I noticed that the positive cable connected to the starter solenoid was able to be moved easily by hand - it was the rear nut on the starter solenoid that was loose, not the front nut, and this allowed the wires fastened here to move clockwise easily when examined by hand. I tightened that up and replaced a couple suspect battery connectors in the battery bank, installed the 2 new batteries, and verified all 4 batteries were at 12.9 volts. This was right before the 2nd stall the other night where I had to disconnect all batteries to stop the spinning of the starter and possibly the air compressor too (2 things stayed running after that stall). Since then I have looked for other loose wires and began examining ground points but have not yet found any other loose or corroded wires. None of the batteries were negatively impacted this time.

I am beginning my studies using "Mid/Heavy-Duty Truck Electrical and Electronic Systems" by Robert N. Brady and by trying to learn here. Overall, this M920 is lightly used and have not yet seen any noticeable loose wires or grounds or rusted/corroded wires or grounds. This truck has been in a much hotter and much more humid climate for the last 17 months. I ran it at least once a week up until 2 months ago. I always disconnect the batteries after running the truck as there is a weird constant draw from the speedometer (which I will replace with mechanical tachometer once it arrives with the new cable). The only thing that changed in the last year is the tachometer stopped working after fluttering around a bit, so I am also unplugging the speedo/tachograph until I can hook up a manual tach.

I have not yet found this exact scenario in my searches on the 5 ton and up forum threads, but other searches suggest starter relay, starter solenoid and possibly ignition switch may all need to be replaced. I also need to learn the full wiring diagram and start performing many other tests before trying to hook up the batteries again.

Any insight and direction will be greatly appreciated!

 

[NDT]

920s are negative ground. The starter uses huge amps so if you are connecting batteries and the starter solenoid is stuck and powering the starter, there will be a huge spark at the battery terminal when you install the terminal on the post. The air compressor is direct gear drive from the engine.

 

[farmer73]

Thanks NDT! There was a huge spark at the battery while connecting.

The compressor must have stayed running the previous time since the engine actually started that time. This last time it was only the starter with sparks at the battery.

 

[farmer73]

And, the spark at the battery was when engaging the main heavy gauge Positive terminal that runs from the starter solenoid, without ever connecting the main Negative cable that comes from the starter.

When I disconnect the 12v Positive feed but still wire up the rear battery bank for 24V, connecting the main Heavy gauge Positive connection does not cause a spark, but when trying the connect the main negative from the starter, a much hotter spark occurs (again, this was without the 12v truck feed connected)

I have ordered a John Deere Starter Relay RE170320, but I cannot find a Pollak LS104WP-1 nor a Pollak 31-164 ignition switch. Even if mine test out okay, I think having backup is a good idea.

Anybody have other ignition switch options that work well on the M920?

Also, I believe my starter solenoid is stuck or defective (I may have fried it when removing the 12v feed from the batteries to the truck). It aslo may have gotten stuck if/when the starter relay went bad (got fried by a loose connection later found at the starter solenoid)

Thanks!

 

[NDT]

Suggest you double check which cables are which in the battery box.

 

[farmer73]

Suggest you double check which cables are which in the battery box.

I did check them and just checked them again. Followed them back to the starter and starter solenoid:

1. The Main Positive cable at the battery bank runs to the starter solenoid
2. The main Negative cable from the battery bank traces back to the starter

 

[farmer73]

I did check them and just checked them again. Followed them back to the starter and starter solenoid:

1. The Main Positive cable at the battery bank (right rear battery POS) runs to the starter solenoid
2. The main Negative cable from the battery bank (left rear battery NEG) traces back to the starter

 

[NDT]

Looks correct. I would remove the starter and take it in for repair. I am also concerned that the spark you got when connecting the 12 volt feed was your alternator getting smoked due to reverse polarity.

 

[farmer73]

Looks correct. I would remove the starter and take it in for repair. I am also concerned that the spark you got when connecting the 12 volt feed was your alternator getting smoked due to reverse polarity.

I will test out the starter solenoid, the starter, the alternator, the starter relay and the ignition switch. I will rebuild, replace, repair as needed.

Thanks NDT!