I went thru this about 4 years ago and have an Alldata copy with my markups...it pretty much describes the system, locations, connectors etc....Unfortunately the whole document is 2.6Mb with the control module under the drivers seat which was not the problem, so cannot post the full document, but attached is the bulk of the design without the module.
I had what boiled down to torn yellow connector (contacts) and separated wires within the harness (brown insulation) under the passenger seat from swiveling.
The wiring goes behind the seat, cross to drivers side at the plywood to front flooring section junction,go to the b pillar and join another harness. I replaced the connector and harness. Wasn't too bad a job...
This may help someone with this very common problem...added a pic of the connected seatbelt restraint system (charge mechanism) you sit next to since it is pretty cool...
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Pac NW and warmer places
1995 E250 EB 5.8 2WD on to a new owner
2006 E350 EB Elect Top 2WD
2000 E350 7.3-I have new seats-but-I kept the ford original seat belt latchs and wiring and bases from ford. But the driver seat latch/pretensioner was never connected to anything. passenger side is connected and working.