Howdy back and welcome.
That van should have two batteries.
The second one is located under the drivers side by the frame rail. a REAL PITA to get at and service.
Because they are such a pain to get at, most people never do anything with it or even know it's there.
Very possible that that battery is toast and/or shorted and the cables are bad.
These diesels use a ALLOT of juice so two GOOD batteries are needed along with good connections and cables.
I would start with checking that other battery.
1996 Chvy 3500 CCDWLB 6.5 Heathed, NO vac, marine injctrs, ARB bumper, BIG pipe, 3" lift, bright lights, bypass oil system.
1986 Chvy 6.2 M1009 blazer RAM AIR, Headers, Custom interior
2001 Chinook RV, V10 gas
1974 John Deere 1530 diesel tractor
1993 John Deere 455 Diesel lawn mower
1967 GTO, 1989 Honda Transalp
2009 VW Jetta TDI, flashed and piped, 6speed, fun car!
1998 6.5 suburban, stock, daughter's
1993 6.5 3500 CCSWLB GM8, Heathed, big exhaust, gauges, Son's
1984 6.2 ATS turbo 3500, SCDWLB - Son's
3 kids, 1 wife, 1 dog
Gunsmith, Tactics Instructor, Fabricator USMC 87-93 Semper Fi!