High beam headlight issue

Headlight circuits are usually on an auto-reset thermal circuit breaker. The fact that it stayed on for a while, went off, then back on-off indicates that the breaker is likely cycling due to an overload.

A short circuit would immediately shut the high beams off and they would stay off. The circuit breaker is seeing an overload that takes a little while to trigger it. Then after it cools enough, it turns the lights back on.

I would try replacing the breaker first. The breakers have been known to be defective once in a while. Check the owner's manual for the high-beam circuit breaker location. It usually plugs into a fuse box or electrical center.

If that doesn't work, you will have to find the source of an overload, which can get time-consuming.

Steve

Find the body ground near the headlight assembly. Follow wiring from headlamp socket to where the black wire meets sheet metal.

Clean ground. Inspect headlamp sockets.

Inspect dimmer switch connector.

I had a issue once with a Mercury Comet on a trip, same thing happened to me. Late at night on Interstate near Indianapolis, lights went off. Put on low beam and ok. Stopped at a small service place, guy said its a bad bulb, checked tail lights and a bulb was out, replaced bulb and high beam ok.....maybe a coincidence but I have always remembered it....

Can you replicate the error sitting still with test light in hand?

I would say it's a bad breaker also. My old Bronco has that problem and it showed up late one night in the middle of the desert on a moonless night. That was probably 8 years ago and I don't think I've ever put the high beams on again.
Some day I plan to address it, but not anytime soon.

Replace the headlight switch. Once they get bad enough it happens on low beams also. When they heat up they kick out until they cool off. It's a known problem on our 2nd gen Rams. 20-25 dollars at Napa, do not buy a BWD switch for this app, I had 2 bad ones in a row.
Watch out for the sneaky screw by the power outlet, pull the tilt wheel all the way down, pull the shifter into low if AT (set the brake first), and pull the bezel gently towards you to release the clips.
That bezel is $$$$ so be careful. All you need is a phillips, 10 minute job.
BTW the new switch will not come with the knob, the little silver spring loaded button on the bottom of the switch releases it.

Why aren't these switches on a good relay for both headlight and tail/marker functions? Direct amperage load-bearing light switches are sorta dumb, ya know. Manifold relay bank bases are available and they look pretty and are neat under-hood.

My 89 dodge ran full headlight current through headlamp switch AND dimmer switch, and I was getting about 3 volts drop over the stock wiring circuit. This was after I replaced the Headlamp switch and Polished the contacts in the heavily oxidized dimmer switch.

When I made a 12 awg relayed harness and lowered the voltage drop to just 0.3v, the increase in the light output was easily 30%, and few cars on the road next to me put more light on the road, and I only have 55 watt sealed beams. I don't care if bulb longevity suffers because of the voltage increase. I do care about having a compliant beam pattern, and I get irritated with the current trends of HID and LED 'upgrades' placed into halogen reflectors which can simply never work properly, and blind oncoming traffic to some degree or another.
with a quality harness and quality relays, any headlight failure is much less likely, but bulb life is acceptably shortened. Id rather see properly than worry about stretching my dollars spent on headlamps by a few months.

Six years later Landy Dodge must have learned, because my Spirit has 2 relays, in the headlight circuit. I did cheat and substitute 100/80 bulbs (Hella) for OEM.

Save your fingertips - beam angle has been adjusted DOWN and no one either Mexican or gringo (in the USA) flashes me. But I am still planning to fit a 240 watt CREE light bar on the bumper when cattle are doing the polka on the centerline.

Did you ever check the actual consumption of those hella bulbs?

I seen a few places claim that they come nowhere near their wattage claims at likely voltages.

Those Lightbars are pretty incredible, but possibly dangerous if abused On road. Their aim is even more important so as to not cause too much foreground lighting, which impairs distance vision, especially in aged eyeballs.