"clicking" under the dash

OK You'll probably find the short circuit in the park switch just inside the gearbox cover. The thermal safety inside the 67 wiper switch is a strip of bi-metal. It will eventually crack in half. Then either replace entire switch or take the switch apart and route the safety out of the switch and attach a cycling circuit breaker on it outside.
Went through all of this with our very first 67 notch. Variable 3 speed wipers.