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On a 1954 3600 new 12v wiring harness, alternator, standard front lights with dual filament running light/turn signals, LED tails/brakes and LED rear turn signals

Went to take the truck out the other morning when it was still dark for a little bit. Truck fired right up, and after a quick warm up i turned the lights on and away I went. About a mile from my house on a paved road i have an option to switch to a dirt side road which i chose this morning. Upon transferring surfaces from paved to dirt I lost all my front lights- brakes/tails still worked. No one else was around and i just rolled back to the house quick and grabbed a different vehicle.

Now as I'm getting around to looking at in daylight this is what's going on:
With the key on, at the first pull of the light switch i get all front and back running lights
At the second pull (headlights) i get what sounds like a power drop on my fan, no headlight low beams, and my running lights stay on like they should
If i push the dimmer switch for High beams both highs come on and my running lights also stay on still like they should
In addition, regardless of light switch position i also do not seem to have any functioning turn signals - these are wired to dual filaments in the running lights

So my guesses/attempts
Everything worked fine lights and turn signals, before i went to dirt, sounds like a power drop with the lows so im guessing i lost a ground or its ground related maybe? Checked everywhere i could think and no loose or dirty grounds, certainly nothing that looked fresh, all wires and connections seemed solid. All fuses were fine. Dimmer switch is a month old but was working fine. Seems odd both my headlight Lows would have gone out at the same time but maybe? Seems odd that all bulbs seem to be getting power so it shouldn't be a ground maybe? And why then are the Turn Signals not working?
Test light shows i have power from the dimmer switch and everywhere its supposed to be when the highs are on but nothing with the lows...


Everything has been in this configuration for many months and worked just fine with no issues up til now
Im stumped and open to suggestions as my electrical knowledge is fairly limited
Thanks in advance
Chooglin

The headlights have been working fine months before?
Are they halogen?
Maybe get a separate ground wire long enough that is
connected to the frame to check both lights.

I'll use my "go to phrase".... check your grounds, or add grounds.

The high beams and low beams use the same ground, so that seems unlikely.

I would be inclined to look for broken insulation on the low beam circuit. The increased electrical system load indicates that a lot of power is going somewhere. A wire just barely rubbed through will short to the body instead of lighting up the lights.

Do you have a fuse for your headlights?

If original, the fuse is in the headlight switch. A short or high amperage drawwould cause the lights to go on then off repeatedly. The switch has a bi-metalic strip that when heated up bends and opens a contact. Once cooled, which only takes a second or so, straightens back out and closes the contact completing the circuit. Thus the blinking lights.

When the new 12V harness was put in, were the headlights put on relays? If so, maybe the low beam relay croaked.

I would unplug on of the headlights, check your resistance to ground, then check the voltage of each of the terminals with the headlight switch on and the dimmer in each position.

You could also have a problem in the dimmer. They get a lot of abuse and are not in the best postion. Meausuring the voltage at the terminals will tell you if you are getting voltage (full or reduced) there.

Either way, that will tell you where to look next.

Chooglin I've had trouble with that bi-metal breaker on the headlight switch too. However ground to the cab that also goes thru bolted joints can bother you too. Guitplayers suggestion of a portable ground wire might tell you a lot,could ground the headlight shell that way. Used to fight ground to the tail lights a lot because of muddy roads and rust.