Hotrod,
I might be able to help ya. I basically constructed a 1982 style delay system in my 69. Had to do much research along the way.
There are three primary items in that system.
1. Switch
2. Relay module
3. Motor.
You say yours runs on high and low speed, but no delay?
Okay, the good news is you can get a brand new wiper switch from NAPA for about $25 or less. It has a built in resitor that can fail over time. I would suggest you start by changing this. Hopefully it does the trick.
The module in the jack area takes a signal from the switch, and converts that signal through a timer that will turn on and off the power going to the wiper motor. The bad news is that unit is about $230! The good news is they are still available for your year model.
The C3 is significantly different than the C4. The C3 uses ground related signals to trigger action in the wiper motor. That is why it has to use that seperate module to use the ground signal and turn it into an on off switch.
In your case, if you had a bad ground the system would not work at all.
Good luck.