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MG MGB Technical - Fog Light Installation

I have installed fog lights on the front of my 72 MGB GT. I have ran the wires to an unused lighted rocker switch on the console just below the radio, just left of the cigar lighter. (this switch may have been used for fog lights in the past I'm not sure).

Currently,(to bring 12v to the switch) I have a wire connected to an unused spade on the fuse block (First from the bottom, which is a brown wire, power always on). My wire has an inline fuse.

This all works fine as is. However, I would rather have the fog lights work only when the ignition key is on. So my question is would it harm anything if I were to connect this power wire to the the unused spade on the second fuse up, (the white wire). Or is there a better place I should be getting the 12v from.

Thanks,
John Fraioli
John F

John. White wire circuit would be my first choice for power. If you have not done so, a relay to supply the power with the switch activating the relay, seems to be the preferred option.

Les
Les Bengtson

Here's a link to a topic where I made a three posts providing instructions, options, and a schematic for installing driving lights. I would wire fog lights the same.
http://www.mgexperience.net/phorum/read.php?1,559498,559607#msg-559607
Kimberly

I would recommend powering the fog lights from a relay, with the power for the lights coming from a fused brown as it is now. One side of the relay winding could then be connected to an ignition feed i.e. green, and the other to the rocker switch, which connects a ground to the relay to operate it.

Powering the lights from the white puts all the load through the ignition switch, which isn't a good idea.
Paul Hunt 2

Paul. I am having trouble understanding your recommendation to use the green wire circuit, rather than the white wire circuit, as the source of power to trigger the relay. Something is not clear here.

The green wire circuit is a fused circuit with its power input from the white wire circuit. Thus, hard to see how using the green wire circuit would result in less power draw from the ignition switch. All I can see it doing is adding an additional load to the fuse between the white wire input and the green wire output circuit. Thus, running the lights, directly, off either circuit would put more of a load on the ignition switch. Running a relay would put a minor load on either circuit, but an additional load on the fuse for the green wire circuit if it were wired to the green wires.

What am I missing here?

Les
Les Bengtson

Les (I'm channeling Paul Hunt 2 here, so bear with me)

"White wire circuit would be my first choice for power." sounds like you plan to supply power to the lights on the white circuit. You may have meant to use the white wire circuit to power the relay, not the lights. Since the white goes through the switch it is not the best choice to provide actual power to the lights.

Paul is saying, a better choice is to use the Brown circuit (fused) to power the lights via a relay. The relay, if wired to a circuit that is switched to the ignition (such as the green circuit). i.e. the small switch current from the green circuit via the unused subpanel switch actuates the relay, which acts as the heavy duty switch and wiring to supply the actual power (fused, brown) to the lights themselves.

Hope this makes sense. It does to me. lol

dave
Dave Braun

John

Suggest that you power the fog light switch from the low beam headlight circuit. This allows the fog lamp to be used only on low beam. You don't want to use the high beams if you want to see anything in fog. Conversely, if you are installing a driving light you power that switch from the high beam circuit. Turns the driving light off when you dip your headlights for oncoming traffic. Many states have laws that mandate this type of "control" on fog and driving lights.

FWIW

Larry
Larry Hallanger

To wire the lights as Larry suggested, use the schematic in the link I provided above with one exception. Instead of a white wire from the ignition switch going to pin 85 on the relay, splice into the blue/red wire to supply power to the switch that goes to pin 85.

Here's the link to the schematic.
http://www.mgexperience.net/phorum/read.php?1,559498,559607#msg-559607
Kimberly

Personnaly I wouldn't (& haven't) used any of the above! Isn't it prudent not to tamper with the original working circuitry and power additional lights independantly? Why modify existing working wiring with taps & add ons? My thinking is that your asking for trouble & a fire may indicate to you that you got it wrong. :-(
Check out this diagram that I used with the power feed straight from the battery >
http://www.bestimageupload.com/viewer.php?file=4tozrmxwygmzttky5io2.jpg

Here's another option in that the foglamps can be set to automatically light upon normal light operation>
http://www.bestimageupload.com/viewer.php?file=unimj2xjvrmwiy5gmtmz.jpg

Heres what I used them for>
http://www.bestimageupload.com/viewer.php?file=czj3hm32jitq4hiznzyl.jpg

HTH

Paul

Thanks to everyone for all your comments and tips.
There seems to be a lot to absorb and some diffrences in opinion.

I have posted questions on things in the past and have always respected and appreciated the responses. I have not always followed thru with posting the results that I have achieved after carrying out the work.

I have been spending all my free time lately working on this new project of mine...this 1972 MGB GT that I purchased just 6 weeks ago. It has been my daily driver since I bought it. I have been receiving emense pleasure driving and working on this car and will continue to use it as a daily driver in place of my 1998 Toyota 4-Runner which I will use during the fall/winter/spring blizzards that we do receive here in Colorado.

I will have to study all the comments carefully and decide which way to proceed. It appears that the only advantage of using the rely is that the "load" current will not have to travel through the rocker switch. Is this correct? Per Paul's advice I will not use the white wire circut for power unless I incorporate a rely. That way I will not be putting stress on the Ignition switch. Am I correct in assuming that the way I currently have the system operating the only harm that might occur is damage to my rocker switch by having load current travel through it?

Just to let everyone know. My horn is now working and I did pass my emission test 2 weeks ago( I did fail terribly the first attempt 3 weeks ago). I have not yet tackled the hazard lights which are not quite functioning correctly.

Thanks again for all your help.

John Fraioli
1979 MGB
1972 MGB GT (daily driver)





John F

John-
You are correct about relays reducing the load through the dash switches. In the late '70s the factory was doing this when an ignition relay was incorporated.

Paul-
I don't see the difference between the diagram I supplied and the first diagram you supplied. Brown wires are directly connected to the postive battery cable.
The second diagram you supplied is a combination of the diagram I supplied and the instructions I gave for substituting the headlamp circuit for the white circuit going to pin 85 on the relay. A nice option.
As suggested to me, what do you think about using switches that self illuminate when closed?
Kimberly

Kimberly Yep You have a point but me not so good on electrics. I think you posted your diagram just as I was writing my reply. (10 mins!) Hopefully with all our input John F. will be illuminating some dark country roads soon.
Paul Morgan

Dave Braun has it - the green circuit is simply providing power to the relay, which is minimal. Power for the *lights* - which is much higher - is coming from the brown circuit and not via the ignition switch, that is the difference.

When talking about *fog* lights it is very much counter-productive to power them from the main beam as they will cause a total white-out in fog. Even dipped beam renders fog lights pretty useless, which is why I have mine available with the sidelights, both front and rear.

With spot lights on the other hand, it *is* sensible to have them available only when the headlights are on, and possibly only main beam.
Paul Hunt 2

This thread was discussed between 16/05/2007 and 18/05/2007

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