1st off did you gap your plugs or did you buy them already gap. You might of had a bad plug,i never heard of bosch plugs don't work in a ford.

go threough the wheel wells only the back one is hard that way

on my 4.0 v6, the front two plugs on each side i get to by taking front wheels off and going thru fenders. Very easy that way. The rear two, i have to go up from below the car, using just a plug socket pushed onto the plug, and turning the socket with an open end wrench on it's flutes. You can touch the plugs from inside through the doghouse, but i'm not able to rig a combo of wrenches that work from there. Suggest going with premium platinum tip plugs, and putting anti-seize on the threads if you plan to keep the van. I'd bet many aerostars have never had the rear plugs changed. on the plug wires- my '96 4.0 has a coil pack on the passenger rear side. I changed one wire at a time- using the silicone grease to seal them. What year/engine?

My 96 3.0 also has a coil pack...I think it's easier to work on the plugs on a 3.0 over a 4.0 as I can get all 6 plugs via the wheel well. The 93 is distributor but the plugs are just as easy. I too put aluminum antiseize on the plugs, a habit I got into owning VWs.