No its not a safety feature.
I had headlight issues to. They would randomly turn on and off while i had the switch on. Id recommend replacing the headlight switch. I have a new one ill be putting in this weekend to hopefully fix my problem. ive read that the headlight switch construction and technology is not the best in early mustangs. its a good place to start troubleshooting it and a new switch is cheap

 

#1The early wiring technique combined with a mediocre switch aging wire and questioanable grounds isn't a good recipe. A relay will help.
#2 As for the OP's situation.? Maybe not enough power/amperage to the bulbs because of #1

 

I'm not sure what the point of it is, but if you are the proud owner (ahem) of a 1981 VW Rabbit you can't turn the headlights on without the engine running. For some weird Teutonic engineering reason.

Not normal for an old Ford at all, you should be able to turn the headlights on anytime. Even if the keys are in your pocket. Something pretty odd has happened. I wouldn't blame the switch. The headlight switch should have power to it any time the battery is in the car and the cables hooked up. I wouldn't think (or hope) it would be too terribly hard to figure out with a wiring diagram and a test light.
Will the headlights come on with the ignition switch "On" or does the engine actually have to be running?

 

I'm not sure what the point of it is, but if you are the proud owner (ahem) of a 1981 VW Rabbit you can't turn the headlights on without the engine running. For some weird Teutonic engineering reason.

My "Japanese" Subaru (built in KY) has this feature. I never turn the lights off.

 

It might be with putting in a switch for a 69 (4 light) to handle a bulb upgrade in the future. I did and it works great. May not fix your problem, but it may, and it’s a nice way to future proof things.

 

FYI, a 67 Cougar HL switch was rated for higher amps because it had a 4 hl system, so that switch will work too.

But for OP's orig question, I too do not think it's a bad HL switch.

Flickering HL's and lower speeds can also be a bad/weak orig style voltage regulator. The reproductions not great. Switch it to newer electronic regulators.

OP, have you taken out or changed anything lately like ignition switch? High dimmer switch? Or starter switch and wires not in correct location?

HL power wire I believe is a #37 on schematics, a black with a yellow stripe, comes from fuse panel to starter solenoid, to head lights. So if you have that wire to wrong post on your solenoid, that'll cause your issue..

 

It just started happening recently. Car must be running or no lights. I have noticed that the low beams flicker sometimes when driving andtue high beams don't seem to flicker.

Maybe I should just rewire it. I just get annoyed with wires and taking dash apart. I have aftermarket lights with led bulbs that have a harness that plugs into the orginal harness. I guess it's time to take it all apart.

Not related but also noticed the door unlocks when you close it while locked. Then one day it suddenly stopped doing that feature and I locked myself out.

 

My first bet is a faulty switch... but before you replace it, check all the wires for worn insulation. Something touching something that it's not supposed to be touching can make funny things happen.
Way back when I first bought my car I had it out for a stroll late at night on the back roads. Had the hi-beams on for a few minutes, then everything went dark. After a brief panic I switched to lo-beam and the lights came back on.
One wire on the hi-beam lamp harness was worn through.

 

Maybe to much driving in the rain ?

 

I too think it sounds like the OP has a voltage regulator problem.

FYI, for anyone replacing the headlight switch, I highly recommend ordering a Motorcraft switch and nothing else. I tried three examples of another vendor's headlight switch and couldn't get the knob to clip into any of them. The knob clipped in just fine with the Motorcraft switch.

I ordered my Motorcraft switch from my local O'Reilly. It was a bit of a challenge for the guy behind the counter. Apparently it's a "special order" part. But they can get it and I got it after a few days.

Be sure to save your old headlight switch. You will likely have to break off the angled mounting adapter and graft it onto the new switch. The Motorcraft switch comes with a flat adapter which I don't think works in a Mustang. It sure doesn't work in a 1970 Mustang! (Oh yeah, replacing the headlight switch was a 4-week job. And people wonder why it takes so long to restore a car.)

 

I think you maybe correct about the regulatory. Im not quite sure yet where it is located. The car has a small blue box under hood I always thought was some cheap ignition box but maybe it's the regulator. I'll have to examine it closer. Any recommendations on a great brand or quality regulator? I see they are fairly cheap on summit for aftermarket replacements so it wouldn't hurt to replace it just to eliminate that possibility.

 

Your voltage regulator next to radiator, drivers side.
The orig 67 type were mechanical points inside. Has about 1 3/4" high cover
https://www.npdlink.com/search/products?search_terms=voltage+regulator&top_parent=200001&year=

Recommend going with newer design "electronic" ones, Cover only about 1" high.
https://www.npdlink.com/product/vol...ackurl=search/products?search_terms=voltage%2Bregulator&top_parent=200001&year=

As for your starter solenoid, it's mounted next to your battery.
https://www.npdlink.com/search/products?search_terms=starter+solenoid&top_parent=200001&year=1967
If you've mixed up the smaller wire on this solenoid, it'll most definitely cause your "headlights on" only when running.

 

Make sure the battery connections are clean and good. I had an old Chrysler that developed the opposite problem- the starter wouldn't crank unless the headlights were on. There was a less than perfect battery connection. Check the grounds...

 

Do the tail lights come on when you pull the switch with the car off?

I'm just wondering if the problem might be something related to your LEDs instead of the switch. Like maybe they're not getting enough voltage to run with the car off due to the old wiring, bad connections, etc.

Incandescent bulbs will run on low voltage, they'll just be dim. LEDs might not even turn on at all. Just a thought.