Yep, wasn't regulated until later when they decided that the running lights should stay on. Especially handy if a headlight burns out and an oncoming driver does not have to think about whether you're a motorcycle or a truck!
However, maybe on the '66 switch, and for sure on later replacements, the extra contact tab was in place. Just not connected.
So you can find the front running lamp wire, move it from one position to the other and voila! They stay on.
We often did it to our sixties passenger cars, but I've never tried it on a Bronco before. If you're interested though, you can dig into it a little more.
Just one of the many quirks of a vehicle made prior to the implementation of 90% of the safety regulations to come into play later.
Paul
