International DT466E Will Not Crank

Hello! I recently purchased a 2008 International Navistar CE300. It has a DT466e engine and an Allison Automatic Transmission. Here's the story: I went to pick up the bus, and the batteries were dead from sitting for a year. We charged the batteries and the bus started right up. I then drove it about an hour home. I've since started it a few times to move it/show people with little to no issue. Recently however, I have run into an issue where the bus no longer cranks over. Here's what I have tested and what I have found:

• Battery is charged and was jumped to a running car (just to be sure), volt meter on dashboard says about 13.7v.
• No warning lights on dash, dashboard initialization sequence seems the same as when the engine still did run (I get the Red/Yellow Engine warning lights, so ECU appears to be booting fine)
• When turning the key, I hear a few clicks from relays, none however seem to indicate that the starter is drawing any power (and amp meter hardly drops at all).
• I have removed power to the batteries and reconnected to cycle any soft safeties that may have been triggered (emergency exits, LNCB, etc)
• Tested Output of Starter Solenoid, appears to open properly, tests 12v on starter side when key is turned.
• Starter Solenoid, when jumped with a wrench, only emits a tiny spark when bridged, I would expect a much larger spark if starter was attempting to engage. No sound is made from starter indicating it is trying to do anything
• Attempted lightly tapping on starter in case that magically worked
• Tested continuity between engine and the same ground point (a screw that attached a wiring harness passthrough to the firewall) I used when I tested the solenoid and got no continuity
• Thus, Seems there is no ground to the engine?
• Looked under bus by battery box, one thick cable appears to exit box and attach directly to frame
• All 3 battery connections are tight and voltage/continuity checks across all batteries and jumpers
• The 175amp fuse under the hood and above the engine tests fine, but the terminals on either side are severely corroded/rusted
• Checked every fuse/breaker in the side fuse panel beneath the drivers window, as well as above where the engine is located,
• Checking the Accessibility Lift's positive/negative leads (used to work) I get no voltage. I Didn't check when key was in accessory.

Any help is appreciated, I am new to these International controls, and I am at a complete loss. Thanks in advance!

 

Thanks for the reply. I can't seem to locate any rear door lock, or any indicator that this bus ever had a rear door lock. When the transmission shifter is moved, the "_" under the selected gear on the dashboard moves. I checked the 3 fuses in the battery box, and the inside of each waterproof holder looked like they rolled off the factory floor yesterday. (The fuses tested functional as well.) I haven't checked the solenoid switch wire yet, but I did test that the solenoid opens when the key is turned yesterday by testing the voltage on the output voltage of starter side of the solenoid.

Another interesting note, when the key is turned to the start position, the amp-meter actually moves closer to zero, rather than further away.

 

I do not have that rear door latch. I load tested my 3 batteries and replaced 1 bad one, but still no crank. I'm lead to believe I have a dead starter. I bridged the 2 fat terminals on the solenoid by the starter and still no noise or anything. I checked that the solenoid is getting power and ground, and when the key is turned into the "start" position, I hear a faint click from the solenoid and the output pole measures 12v.

 

Thank you all for the suggestions. I replaced 1 battery, charged all 3 separately, tested continuity everywhere, wiggled the shifter, alongside triggering every safety that I know of on the bus. Miraculously, it has now started. I'm not sure really what was happening, but hopefully it happens no more.