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1950 3100 stock 6v system

When headlights are turned on I have no low beams. When dimmer switch is pressed, driver's side light comes on but passenger side stays dark.

Taillights and brake lights work. Instrument panel lights work as does the high beam indicator.

Taillights and front running lights also work when switch is pulled to first detent.

Headlight bulbs are new 6v units.

Dimmer switch was removed and all contacts cleaned and de-grunged. No bad corrosion was present, however.

Where do I look first for the likely cause? I'm inclined to believe the dimmer switch is bad but before I buy one for $20 or whatever I figure I''d ask here for the likely suspects. Battery and cables are all new and clean, etc.

Original T3 bulbs worked but were dim.

What is the condition of the wiring to the lights? Do you get power to the connection block on the left and right side fenders? If you do the problem is between the block and the light. I believe there is a ground on then the fender well too. I think you just have to get the test light out and start at the switches and see where you have power and where you don't.

First, test the bulbs. "New" and "good" are not always the same. A hot battery and a set of jumper wires is the most effective method. How did you get inside the dimmer switch to clean the contacts? The ones where the wires attach usually aren't the source of a problem. Once you're sure the components are good and working properly, start wringing out wiring with an ice pick test light. Be absolutely sure the grounds for both headlights are clean, tight and not corroded. Getting voltage to the lights is only half the battle- - - -the current has to find its way back to the battery.
Jerry

I did not disassemble the dimmer switch.

Interestingly, when I clicked the dimmer switch on and off a couple times, the driver side light became less bright.

The wiring in the truck overall is remarkably good. The insulation isn't cracked and flaking off and the wires are flexible. When this first materialized I swapped bulbs side to side with no change in results. Driver side worked on bright. So it seems that both bulbs will light up.

The dimmer switch is probably part of the problem, but I'm prone to suspect bad grounds, etc. being responsible for some of the trouble. A high resistance or nonexistent ground path causes voltage to back up through places it's not intended to go and cause all sorts of sneaky gremlins to appear out of nowhere- - - -usually intermittently.
Jerry

Where is the primary ground for the headlight circuit? Does each light have its own in the bucket somewhere?

I think the wiring for each headlight has its own ground that attaches to the inner fender near we’re the wiring blocks are on the inner fender .That is how my 54 is .

Otto,
Hello again.
Take a look at the wiring diagram and you will see a ground by each Wire Panel going to the headlights. As stated previously, this may be your problem
Harold
http://chevy.oldcarmanualproject.com/electrical/wiring/pdf/50truck.pdf

One of thre three pins on the back of the sealed beam is the ground. Use a set of jumper wires and a battery to wring out which blade terminal is the common ground which allows the high and low beams to burn when power is applied, and trace that wire in the 3 pin plug to the point where it attaches to the body metal. Be aware that decades of rust can interrupt the normal pathway back to the battery, so adding a few extra ground wires can definitely be to your advantage!
Jerry

My first though, which was wrong, was that the ground would be the center terminal. I now have a diagram which I will share.

Thanks for the diagrams Harold and Phil. That's today's task.

Harold, I haven't removed the steering wheel yet to check out the mast bearing/wire connection for the horn but that's also on the to-do list soon.

That diagram's saved to my computer now- - - -I always forget which wire is which!
Thanks!
Jerry

Jerry,
Here is a couple of diagrams you may wish to save to your PC also.
The first one is for the 2 wire horn, the other is for a 1 wire horn.
Harold