Ford Repair: lights flickering/pulsating, ford f 250, voltage regulators

Question
I have a 1973 Ford F-250 with a 360. The lights pulsate all the time. The faster the RPM's, the faster it pulsates. I have replaced the battery, alternator and tried a few different voltage regulators(which I believe were all from NAPA). I have added ground straps to both the battery and engine and have crawled inside and out looking for bad grounds. I do have a bad light switch that shuts off after a while of use in high beam-- don't know if this could cause my problem or endanger the new switch I have for it??  Please HELP!! I'm getting Crazy Eyes! --- Also, my horn only works once a day!??! After it honks the first time, that's it for a while.

Answer
with a voltmeter hooked up what are actual voltages outputs with lights on and off-was this doing this before any components replaced-try a ford regulator-replace light switch regardless. horn could be connection problem or weak relay. if you can't figure it out have it checked out. good luck.