Need help!! Freightliner with Cat 3406e got me stumped

If you could find a way to give it the 12V supply, 12V ignition, and battery ground, then see if you have any sensor supply voltage out. Should verify quick if the female terminals coukd be your issue

 

I meant with the vehicle harness off of the ecm, and give 12v and ground to 4, 5, 6, and see if yoy have sensor voltage.

 

If it does have sensor voltage that way, but not with the vehicle harness connected, the 4, 5, or 6 terminal of the vehicle harness would seem the problem.

 

Check for the 5v signal at your coolant level sensor, that's on pin 36. That 5v signal comes out of the ECM.

It won't be there if ypur ECM isn't powering up. Then if you hotwire it on 4, 5, and 6, and you have 5v at pin 36, your harness pins are your problem