Where would you find a intermittent wiper control box for a 1976 f100?

According to Fordification.com... "Installing a factory Ford wiper delay setup in your classic pickup is one of the little things that make day-to-day driving so much more convenient. Ford did not start using these until '78, but the good news is the '78-'79 setups will plug right into your existing wiring. Look for these setups in XLT Rangers and Broncos." http://www.fordification.com/wiperdelay.htm Installing a factory wiper-delay setup by Chris Pate and Keith Dickson