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CHU MP8 Dead outside the firewall

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One of my shop guy's installed a new air brake foot valve on 2010 CHU613 MP8 while it's in for winter service.  The truck would not crank when we tried to move it out the shop.  He disconnected the large square wire harness at the firewall in order to put the foot valve in.  The dash powers up.  Lightning bolt is on.  Starter will not run.  The pto/airslide,wipers,rear light's are all non responsive.  The headlights at the front on the hood are functioning.  A am also unable to connect my service tool now.  It's acting like the key is switched off.   All fuses are good.  I've inspected the harness at the firewall and the wiring to the key switch and under the dash.  Don't see any problems.  I'm at a loss.  Relay or issues with the fireawall connection or harness.   I have no diagram of the harness.

Ideas or thoughts?  Thanks in advance.  

Edited by jwmcgregor

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Thanks challenger.  I’ve taken it apart examined it out it back together.  I’ve checked main power relays and all the fuses in both the BEC and the EPDM.  I’ve swapped the VECU into another truck to check it out.  Everything if ok. 

I hane not swaped  ECM.  Unsure if that could be the culprit.  I feel like it’s in that MC?? Harness through the firewall but not sure how to prove or test it.  

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Resolved....The Deutch connector at the firewall (MC??) had threads smeared when it was removed.  It did not install together properly as the jack screw did not pull the Deutch connector together all the way.   Repaired with tap and die.  The molded nut in the deutch connector on the firewall side will spin in its molded housing.  Looks like a "be careful spot"

Thanks again Challenger!  

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