Welcome to iRV2 .
Have you had the hatch open to look into the engine compartment from the top?
The wiring length from the main harness will limit the location , and I'm pretty sure that length wouldn't allow it to reach forward, of the differential, to a pass through.
Do you have a chassis manual that would describe the PDC/PDM , or gives a fuse lay out, so at least you know what to look for?
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.