Optional item in 79 Vans for sure. I just added it to mine a couple weeks ago (still need to buy the correct motor though).
On the 79 it was a separate harness that plugged into the existing one via a 3 way molex, add the correct switch, add the 5th wire to the wiper motor and swap the motor.
On my 85 parts van it was a more 'built-in' install from the factory and that is where I got my parts from. So I trimmed out all the wires I needed and using some molex plugs from radiohack to make it as close to a 79 type install for future troubleshooting needs if it ever arises (hopefully it wont)
