Take the jumper cables and connect them to the POS & NEG in the Transit van.
At the dead battery, connect the red clamp to POS battery post and the black clamp to a bracket somewhere on the engine.
The reason for this is, when a battery goes dead it creates hydrogen gas. If you make the last connection at the NEG post on the dead battery, this may cause a spark. And that can cause the battery to explode.
If you make the last connection somewhere on the engine, you greatly reduce the chance of that happening.
Tester