Wiring direct is possible but fixing it correctly is rather straight forward.

The fan operates at three speeds controlled by a resistor pack located on the
frame under the radiator. This resistor pack is not likely to be the problem.

Fan speed one operates when the AC compressor is on which is the case when the
heater is in the Auto mode.

Fan speeds two and three are controlled by a thermoswitch located just under the
lower radiator hose on the back of the radiator. The is a common failure and
easily replaced. Cost is usually about $20.

Alternatively, the relays for fan speed one and two are located in the main
relay box under the hood and just in front of the windshield on the drivers
side. The relay for fan speed three is in the auxiliary relay panel under the
dash by the drivers left knee. It is a large double wide relay / controller that
is difficult to remove and replace. The relays for speeds two and three are not
likely to both have gone bad but it is possible.

There is a fusible link just under the brake master cylinder that provides the
ground connection for all three speeds but if speed one is working this is not
the problem.

My guess is that the thermoswitch on the radiator is the problem. You can remove
the plug and short the contacts to test if the fan comes on but be very careful
if you try this because the van is close to the switch and wires.

TonyJ