6V fog light wiring

[Matt Harwood]

 

My project this weekend is to install my new fog lights on my '41 Buick. I'm planning on using a relay (I even bought an NOS Delco 6V headlight relay for the purpose) and using a correct NOS switch on the dash. The factory Buick wiring is arranged so that the fog lights will only work when the low beams are on; switching to high beams turns off the fog lights. I'd much rather go simple and have the fog lights independent of the headlights so I can use them whenever I want. I have two questions:

 

1. The original fog light switch has three terminals on it. What is the third one for? Two makes sense, but I don't know what the third might be. I have been unsuccessful in finding a specific wiring diagram for it. The switch has a fuse of its own, so I figure I'll run power through the two terminals connected to the fuse. The third, is it a ground or maybe the cut-off from the high-beam switch?

 

2. Where should I pull power for the lights themselves? Using a relay, I'm going to pull power for the switch from the ignition so that when the key is off, the lights are off. Since this will only be a tiny amount of current, it shouldn't overload the ignition switch. The relay will pass the heavy current to the lights but I need to figure out where to pull +6V for the lights. Some sources suggest simply taking it from the battery or starter solenoid, but another source says to pull it from the hot side of the ammeter. I suppose I'm really asking if I pull it directly from the battery, will the fog lights' draw still be indicated on the ammeter?
 

I'll be using 12 gauge wire for the light wiring and 14 gauge for the switch (cloth covered in various colors, with armored cable going to the lights themselves). With 35 watt bulbs in there, it should pull about 12 amps, so 12 gauge wire should be plenty big. The power from the ignition switch to the fog light switch to the relay pulls just enough current to energize the relay's coils, which should be almost nothing, so 14 gauge will be fine.

 

Here's the basic setup. It's not quite accurate since my switch has three terminals (one mystery terminal--a ground?) and the relay is a different shape, but you get the idea:

 

 

 

Here's the wiring diagram for the relay (click to enlarge), and it says to pull power from the starter switch or battery (this is for high-beam headlights, but it's the same basic setup).

 

 

Anyone have a '41 Buick with factory fog lights who can shed a little light (LOL)?

[Bloo]

36 minutes ago, Matt Harwood said:

2. Where should I pull power for the lights themselves? Using a relay, I'm going to pull power for the switch from the ignition so that when the key is off, the lights are off. Since this will only be a tiny amount of current, it shouldn't overload the ignition switch. The relay will pass the heavy current to the lights but I need to figure out where to pull +6V for the lights. Some sources suggest simply taking it from the battery or starter solenoid, but another source says to pull it from the hot side of the ammeter. I suppose I'm really asking if I pull it directly from the battery, will the fog lights' draw still be indicated on the ammeter?

 

The battery is the worst possible place.

 

The goal should be to get to the highest voltage point in the system, and that is only the battery when the engine is off, or idling with the generator in cutout. Otherwise the highest voltage is at the generator.

 

On a generator system, the battery connection terminal at the regulator is as close as you can get, due to the cutout relay, and also the current regulator if you have one, and I am pretty sure you do on a 1940 or newer Buick.

 

The closer you can get to that terminal, the better. Somewhere between that terminal and the battery is the ammeter. The voltage will get a tiny bit lower with every connection as you get closer to the battery.

 

If you are on the battery side of the ammeter, your foglight draw will register as CHARGE, not discharge. I consider this undesirable. If you are on the other side, foglight current wont register at all unless the system is not charging for some reason. Then it will register as discharge, which it is.

[37_Roadmaster_C]

Matt,

Some of the old accessory switches were lighted. If yours is one of those the third terminal is ground. If you have an ohm meter check the resistance through all combinations of two terminals. Do this with the switch both off and on. Even better do the tests including the metal mounting surface as a fourth terminal. The reason for this is that the internal light may be designed to be tied into the dash lights so that the switch is only lighted when the dash lights are on. In that case the ground for the switch would be the metal mounting point. Let us know what you find.

Edited February 1, 2018 by 37_Roadmaster_C
spelling (see edit history)

[Matt Harwood]

No, not a lighted switch, it's the factory-style switch that fits into one of the ACCESSORY slots on the center stack. I have a correct knob that says FOG LIGHTS on it somewhere, but I'll probably just keep the ACCESSORY knob on it for now. It's definitely not illuminated. I'm betting $10 that the extra terminal is somehow connected to the hi-beams. I'm looking through my factory literature and manuals now to see if I can find the details but so far nothing.

 

Here's the switch (which is an NOS piece I bought from our friend here on the board, Auburnseeker):

 

 

It fits in the dashboard on the right side of the speaker, second slot down from the top that says ACCESSORY (this Special has the dash copper plated, which looks kind of cool but isn't correct). The ACCESSORY slot on the left side of my dash already has the windshield washer button in it, but it would make more sense to put the fog lights there, since it's right under the instrument light switch and above the headlight switch. Oh well, probably more room for wiring on the right anyway.

 

[Frank DuVal]

Are the two screws at the back connected to opposite ends of the fuse? It is not clear in the pictures.

 

The law in Virginia is that the fog or driving lights have to be off when the high beams are on. But with the dimness of these lights compared to new car/truck lights, no one will notice! They would only know if there were 6 lights on at once on the front of the  vehicle (quad headlamp setup 1957 and later).

[Bloo]

22 minutes ago, Frank DuVal said:

The law in Virginia is that the fog or driving lights have to be off when the high beams are on.

 

Wow. That is crazy, and shows a fundamental misunderstanding of what the lights do. I am sure glad we don't have that law up here. The whole purpose of driving lights is to extend the range of the high beams. Using them on low beam would just blind oncoming drivers.

 

Fog lights are extremely short range, and would usually make no sense along with the high beams, however there are times it would make sense to use them to light up the shoulder a little more while on high beam. For instance, driving slowly down a lonely country road on some black night, in the rain, looking for an unmarked driveway or turnoff.

Edited January 31, 2018 by Bloo (see edit history)

[Matt Harwood]

I'm not too worried about what the law says--fog lights on an old car are largely ornamental anyway. My goal is mostly to have them operational with parking lights and I don't much care about them actually working as fog lights in the fog or snow. But for simplicity's sake, wiring them separately seems like the right choice. It'll look right and work without worrying about cooking the whole dash.

 

That said, it appears that one of the posts on the back is connected to the fuse, and the other goes into the body of the switch inboard of the fuse--you can see it in the photo of the top view. I'm going to do some continuity checks and if it's a simple on/off situation, good enough. Thanks for the tips!

[Frank DuVal]

OK, Crow eating time. Bloo is right, driving lights on with low beams is crazy!

 

Fog lamps are only to be run with headlamps on low beam:

Quote chapter 70 of the Virgina code:  (1) Fog lamps are general illumination lamps as covered in subsection A of this section. They must burn through the tail light circuit even if on a separate switch. If installed on a vehicle with a four-headlamp system, or a vehicle equipped with driving lamps, they must be wired into the low beam circuit.

 

Driving lights, though, are different: Inspect and reject for: h. Driving lamps are not wired so that they will burn only when the high beams of the regular headlamps are activated;  But you are still limited to 4 lamps (head, fog, driving)  lit on the front: D. No more than four lamps, including two headlamps, may be lighted at any time to provide general illumination ahead of the vehicle. Sorry Quad headlamp vehicles.....

 

 

[37_Roadmaster_C]

Matt,

 

Disreguard my idea. Your switch is a different type.  I am also curious about the two terminals under the fuse clips. My thought is that the switch may have provisions to be used either with or without the fuse depending on which terminal is connected to the power source. Just a thought......

[Matt Harwood]

I did some continuity testing and got interesting results. The post on the rear that's connected to the fuse (the one on the left in the photo above) and the post on top are the two that I should be using to connected as I'm planning. They are connected when the switch is on, disconnected when the switch is off. Interestingly enough, the two posts on the back are disconnected when the switch is on and connected when the switch is off. I suspect this is somehow linked to the hi-beams, either preventing the use of the hi-beams when the fogs are on or somehow interrupting the fogs when you turn the hi-beams on.

 

The two posts on the back are not connected via the fuse.

 

Anyway, I think it should work just fine using the two posts that are simply the interrupt circuit like a standard 2-pole switch. I'll try that first and see what happens. Thanks for the feedback!

[Brass is Best]

If you run into trouble use one of these.

[Matt Harwood]

6 hours ago, Brass is Best said:

If you run into trouble use one of these.

 

In fact, I used one of those to service the hand towel dispenser in one of our bathrooms this afternoon. It jammed one too many times. I fixed it so well that it will never happen again.