I'm not sure what the wiring diagram shown is, but it is not the one GM supplied in the 1978 Electrical Troubleshooting Manual at the time, which is this:
As you say John, it looks a little "involved"! So, out of interest, I assume you do not have the delay/pulse option? Did the car have that feature originally? It was advertised for the '78 model year, but in reality was not available at the beginning of production. Or, was the motor replaced later? And, how do your washers operate - do you need to have the wipers on first?
Incidentally, after '79 the wipe delay/pulse controller was changed and moved location to one of the rear storage bins. The original type, located under the centre console, can now be replaced with a "solid state" type, which I understand is more reliable. The problems with mine were cured many years ago by a new relay, but in the future I may change to the new type.