Sounds like you need a shop manual, unfortunately you'll need the 63 and the 65 supplement. Your truck has been molested, please report previous owners to the Stovebolt Gremlins for just retribution.
You may not need the regulator if the alternator was replaced with one that has the regulator internal to the alternator.
It's not uncommon for the canceling cam to go out on the turn signal switch. The plastic gets' brittle with age. The cams are still available check the vendors links, watch the price I've seen vary $30 for the switch. The question is how much is missing. You say the horn doesn't work. Under the horn button you should find the nut that holds the wheel on and 3 screws that hold a plastic washer and a metal washer. If those 2 washer arn't there the horn don't work. The metal washer shorts (to ground) a copper stud that goes thru the turn signal switch rides on a brass washer.
Larry
