Who's good on electrical quirks?

[GMC Truck]

I helped a friend install a tilt column in his 84 truck and the tilt column did not have the wiper switch in the lever so we made a mount and installed the old style dash switch with the delay. No problem, plugs right in and all is well and works great!
Heres the problem... if he beeps the horn OR turns "off" the AC the wipers make a pass... WTF?? I have check the ground to the motor and even added an additional ground and it still does it. Craziest thing i've seen.
Any ideas?

 

[tRustyK5]

It likely isn't anything you guys did. This era of GM trucks has a long history of "phantom wipers". It's usually the delay module itself that gives a random sweep now and then.

Rene