I never noticed this before until the body shop went to check the fog lamps after replacing the old ones.
We noticed that the fog lights only come one when the brights are on. From my understanding, the fog lights should only come on with the low beams.....is that correct? All of the rest of the lights operate normally. With the exception of 2 dash lights......the hi beam indicator light on the tach and parking indicator light on the speedo.
Could it be coincidental that the bulbs might be burned out OR tied into my fog lamp problem? I've tried researching a good 73 wiring diagram and have zero luck.
I did notice that my 3rd peg connection behind the fuse box is missing a wire connection. Oh and all my relays on the fuse panel work. So what gives?
Thanks for yall help

P.s. I know that the hi beam indicator lamp comes after the hi beam fuse but where and color is unknown.

High beam indicator should be tapped off of fuse #1 (Left-most fuse) and the wire color should be white/blue.

From what I understand, the relay ground for the fog lights should go to the positive high beam terminal (it should actually go to the same fuse #1 that the high beam indicator wire comes from, and it should be the same color wire, white/blue)

With the fog lights and low beams on, and the high beams off, it actually grounds the relay through the high beam filament, but because the current through the relay coil is so low it doesn't light the high beams.

Then when you turn the high beams on, the relay can't ground anymore because there's now +12v going to the headlight, so there's +12v on both sides of the relay coil.

(Also, this system depends on the headlight bulbs being traditional filament headlights, either stock sealed beam or a halogen H4 conversions. LED conversions will be problematic without additional considerations taken into account.)

question: would driving in heavy heavy fog not be preferable to use hi-beams? I mean, you're not blinding on-coming traffic because of the fog, right? I drove thru the night to Fla a few years back (in my XC70 wagon), and got into a major fog bank while in Mississippi, middle of the night... I honestly can not remember but I think I drove (most) of it with hi-beams on, going pretty slowly on B roads. It could be that I toggled hi to lo and jut stuck to whatever seemed better, maybe lo w/fogs. Just trying to remember and learn from those who know better.

High beams tend to spit out more light above centerline, causing the light to reflect off the fog and back into your face, adversely affecting your night-adjusted vision. Fog lights sit lower and are aimed lower, from the driver's perspective you don't see as much reflected light, so you generally see further even if you perceive what you see as being 'darker' because not as much light is being reflected. Fogs/low beams and high beams are for 2 different purposes.

Also depending on the location, some places have laws stating that fog lights can only be used by themselves or in conjunction with low beams only. Other laws include a limit on how many forward-facing lamps may be illuminated at once, for instance on vehicles that have high beams as separate bulbs/enclosures if the high beams are lit with the low beams remaining on, the fog lights being lit would mean that vehicle has 6 forward facing lamps, and most places limit it to a max of 4.

Update:
Reading is fundamental.
I broke out the original owners manual and it said that the parking INDICATOR light on the speedo ONLY comes on when the light switch is on the first detent (parking light only) position. Once in low or Hi beam positions, the indicator light goes off.
As for the Hi beam indicator light, it works as advertised when HI beam position is selected.
Here's where the plot thickens....
My fog lamps continue to come on ONLY on Hi beam.
The only thing that changed was the replacement of the original lamps TO another original 914 fog lamps. I will check and see connections and resistance values on the new and old lamps. I've read somewhere that resistance on these relays is important. More to follow.

Only reason for the change was the metal housing for the originals were rotted out.
What I find also weird is that when I fully engage the light switch, the Hi beams default on. I presume that the low beams should come on by default instead of the Hi beams. The manual doesn't specify that info.
Do yall stock lights work this way as well?
I'm almost considering the idea that my lo and hi wires in my fuse panel might be mixed up. But without a diagram it's hard to know. Smh

My own High/Low beam selector relay is a mechanical flip-flop, and it stays as whatever it was set to previously, even if the headlamp switch or key are turned off.

As far as the fuse panel goes, if you're looking up to the fuse panel from left to right you'll have 4x 8 amp fuses 1, 2, 3 and 4.

1 and 2 are your high beam left/right. They should be all white wires with the exception of fuse 1, it will also have the white/blue wires feeding your dash high beam indicator as well as connecting to your stock fog light relay.

3 and 4 are your low beam left/right. They should be all yellow wires.


Edit: Did a little bit of digging and managed to pull this up.

OK. Just a quick comment. My car seems pretty original, but not being the original owner, you can never tell. My fog lights only came on when the high beams were on. Seemed stupid, but that was how was wired. I moved the fog light relay KL86 to fused power. Now the fog lights come on when I want, even by themselves.

So now that I found a good wiring diagram, I am able to understand the operation of the lights (MY 73). Unless the diagram is wrong, the fog lamps come on with the low beams only (stock).
Unfortunately, the diagram doesn't tell me the exact physical location of the fog relay on the fuse block. With so much online traffic that on many wiring variances on years, can someone tell me which relay is the fog lamp on the panel.
I have 3 round and one rectangle on the panel. Remember this is for a 73.
Thanks!

It'll be one of the round ones. Since the position can be swapped around in the holes, the most surefire way to tell which relay is which is to look at the color of the wires coming off the relay socket.
For the fog lights it should be:

Red with Black stripe
Gray with Red stripe
White with Blue stripe, and
White with Yellow stripe.

Problem resolved!
Posting my findings for other teeners.
Conclusion; broken wire at fog light SWITCH
Symptoms: fog lights only light up with HI beams and fog switch laminates normal.
Operation: Speedo parking lamp indicator at 6 o clock position only comes on at first detent headlight switch. Once low beam of hi beam (2 detent position) is selected, this lamp extinguisher automatically.
Rpm gauge hi beam lamp indicator at 6 o clock position only comes on when hi beams are selected by the stock and second detent position on headlight switch is selected.
Fog lamps illuminate when second detent position on headlight switch is selected and fog switch is selected and stock is on low beams.
Fuse and wire connection is needed on fuse block 1 and 10. Fuse 10 provides the hi current thru the round relay (2nd from the left closest to the drivers door). Fuse 1 along with white and blue wire provide the fog relay the ground through the headlights. If the headlights are missing or modified with a higher resistance, fog lamps will not work.
By default (denergized) the fog relay connects to the Hi beams. When the stalk is selected to Hi beams, that removes the ground (pin 85). Low beams provide the ground for th relay coil (pin 86) 12 volts from the fog light switch which engages the relay.

Of course this is on a stock 73 2.0 Lt.
I hope I'm making sense. Once I saw the diagram it made sence.
https://members.rennlist.com/warren/foglights1.jpg

In my country that's how the driving/fog lights must be wired otherwise you won't pass inspection,they must be switched to only work only from the high beam circuit.
Some inspectors will defect if the lights are on the car but not working,I have had this issue,in one case I just removed them and went for a pass on retest,refitted them later after replacing a faulty switch.

Question, which of the wires was broken at the fog light switch?

Was it the brown-blue wire (terminal 15)?