Coronado electrical issue!

I have a 2016 freightliner Coronado 122SD. Isx15

Power to pdm “under passenger side of the dash” with keyswitch off if you put a test light from the battery post to the ignition post the fuel pump turns on and the gauges cycle. You can also jump from the iso post to ign and the gauges will cycle. The truck was going down the road with a load and died on the driver. I jumped the two posts to get the truck home. I’m running out of options with this truck.

Has anyone ran into pdm issues? Is there a common short to ground that I’m missing?

I feel as if it’s a internal short in the pdm or it’s getting back fed by a different short. If you put the test light on the battery post and put the probe on ignition fuses and some others the light will also light up and cycle the gauges/ fuel pump-provide ignition, and complete the circuit.

Any help would be great