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MG MGA - Fog Lamp Wiring

Well folks, my wife says I should get a license plate that says "MG-A-NL". "Why do you care about what date a part has on it", she queries? "Why does the your car have to be white?" she asks (HDR number). I have gone from being willing to chop up a rusted A and install a V8, to wanting to do a concours restoration to the highest accuracy and standard that can be met.
That being said, here is my first anal question:
On North American cars two fog lamps were always installed if the option was purchased. Along with the lamps, a relay (SB40) was installed also. I presume this was to take the high current load off of the switch. Where was this relay located?
On Barney's fine web site, someone located it on the radiator panel, but I can find no confirmation if this is the intended factory location. Anyone out there know?
James Johanski

The wiring diagram in the original workshop manual shows just one fog lamp (when fitted), and it is wired directly to the switch, ie, there is no relay in the circuit.
However, it would make sense to use a relay in a modern installation. This could be hung behind the dash near the switch, or behind the grille off to the side. You might want to include in-line fuse(s)in the 12V supply from the battery to the lamp(s).
Note that original wiring looms have the fog light(s) wire already in them. It is a red with yellow wire, and should be found behind the radiator grille to the right-hand side.
Regards, Peter.
P. Tilbury

Peter, Yes the wiring diagram shows only one lamp. Clausager states that for US cars if the fog lamp option were ordered that US cars would get two due to regulations and would be installed with a relay. I presume this would be to take the load from the small switch and prevent burn out. The location of the standard fog lamp wiring (behind) the grill might indicate that this is where the relay would go if the second lamp were added, but it also could go some where else if the wiring in the harness were large enough. Does anyone know what the wiring size is for the optional fog lamps?
James Johanski

This isn't just about the switch. The fog lamp wire in the harness is the smallest size wire, therefore capable of supplying current to only one fog lamp. When two lamps are installed it needs a larger supply wire. The expedient solution is to run a larger wire from some battery supply point to the front, and switch the relay with the original small wire.

As a matter of convenience the relay goes up front because that's where the switch wire is - also because by tradition an accessory relay goes close to the load so it is easy to find for maintenance purposes. In practice the relay can be physically located anywhere in the vehicle, but placing it anywhere else would require longer runs for wires, and the relay would become logically hidden.
Barney Gaylord

James,

Regarding the Fog Lamp Wiring: Open the "Original MGA" and look at the picture of the red Twin Cam engine bay. On top of the radiator shelf you will note the location of the fog relay. As far as the wiring harness is concerned: Find an early MG-B wiring schematic. As far as having a wiring harness made up: Contact Rhode Island Wiring. Bread board the lengths and give it to them. They will make you a harness that looks factory original. One final note:
Proper lamps are one of each type. One fog and one spot. The fog goes on the road side and the spot on the curve side. If you need to find a relay: Check
Don

James,

Continuing my message: The relay is readily available. The black Lucas cover on the other hand is totally unobtainium. If you take the time to look at original BMC pictures of MG's and Healey's, you'll note that the relay was either mounted on the firewall or heater shelf.
Don Tremblay

Don, I have not been able to locat the proper SB40 relay. The Clausager picture I believe is for the optional flasher switch. When I look closely at the picture I see one brown and one blue wire. The fog lamp and for that matter the spot lamp wiring would be a different color. Additionally, two fogs were only for the states. Laws at that time did not permit asymetrical lighting arrangements. Of course in Great Britain, the single fog and companion spot is correct. (I think--never too sure of these things)

Barney, I believe you are correct. Didn't know if the wiring or the switch is the limiting factor. With the wiring the limiting factor, the relay must go on the radiator panel.
James Johanski

When I installed a spot and a fog about fifteen years ago, I replaced the fog lamp switch with a headlamp switch, and used the first position for fog and the second position for both lamps. Still seems to work ok. Marvin
Marvin Stuart

With original wiring setup the fog light switch draws power from the parking light circuit, so the fog lights go out when the primary lighting switch is switched off, even if you leave the fog light switch turned on. This arrangement then has ALL of the vehicle lighting load going through the primary lighting switch, including the (single) fog lamp. This is another reason to use a relay with dual fog lamps, to reduce the load on the primary lighting switch.

On the other hand, you could move the fog lamp supply wire from the lighting switch parking light terminal to the lighting switch input terminal. This would remove the fog light load from the primary lighting switch, but then you have to remember to switch off the fog lights separately from switching off the headlights and parking lights. The problem of small size wire still remains on the fog light circuit without a relay.
Barney Gaylord

James,

Google Bill Tracey (Tracy). He sells Jaguar XK parts. He has the relay in stock.

Don
Don Tremblay

I spent a bunch of time on this problem, the results of which are what you see on Barney's site. I found original documentation from Lucas about how to use an SB40 to hook up fog lights, and I copied that wiring. It didn't specify where the relay was to be located, so I put it close to the lights. British Wiring has SB40s (or did when I installed my fog lights). If you're being really anal, don't forget that SFT576 lights for your car would be date-coded (MMYY) and the lamp eyebrows for your vintage don't have ridges.
Mark Lambert

I recently went through the foglight installation on my 1600. I didn't have any problem finding the Lucas relay (I bought three). I ran a #10 supply wire with inline fuse from the starter switch to the relay which I mounted on one of the conepoint wing mounting bolts on the passenger side (I put in a longer conepoint to have some extra exposed threads in the engine compartment). The wire runs about 6" down the battery cable then loops upward to the relay. The ground wire was run to one of the bolts on the heater shelf using a ring terminal.

The switch wire is #16 and runs from the front of the harness back to the relay following the path of the harness (through the support struts and grommets on the passenger side). This just hooked-up using a standard lucar fitting as if for a light.

Supply wires from the relay run likewise from the relay to the space on the passenger side ahead of the radiator bulkhead where a second #10 wire is joined to feed the driver's side light. This second wire passes across the radiator under the strut (bonnet locking platform)that holds the bonnet latch and goes to the driver's side void above the shelf.

Both wires pass through the shelf using the grommets for the wiring bundle and loop under the wing/body panels. Grounds for each light were mounted underneath up front.

This installation has some advantages: it does not disturb the original appearance of the engine bay since nothing shows (the wires are all black (color coding at the ends), the dash switch operates the lights, no harness wires get cut so you can "undo" it at any time, you can position the wires that run along the harness so that they ride behind the harness and, with the use of black "zip-ties" even the mounting supplies "disappear", and when you replace the heater air supply duct there is another level of covering. The statements some have made about having the relay near the load makes sense, but having it near the starter switch in the engine bay is exceptionally convenient to work on.

My plan is install a like rig for my halogen headlights by mounting the other two relays on the next conepoint bolt back from the one that holds the first relay. A similar wiring scheme will supply juice to the regular and high-beams that are 'currently' very dim.

Gary Hattwick
1960 1600 roadster
Gary H

Mark, British wiring has only 6RA's now. Same functionally as the SB40 but a bit small and without the screw connections. I found a good reproduction SB40 from Sports and Classics. They advertise it as a Healey overdrive relay, which was another application for the SB40. I believe that you are correct in the installation and am thankfull that you had some documentation to back it up. I am going to duplicate your installation. The relay came today it is marked Lucas and SB40, has screw terminals but no date code. All in all, a nice reproduction--now if I can just find my date stamping tools........
James Johanski

Mark, one more thing. I do have date coded 576's--no ridges on the crests and they even have the bakelight bulb holders!
James Johanski

I don't know that the relays were date-stamped. I don't think mine was. Would have been sort of like date stamping a brake light switch. I think they only bothered with more substantial items.

Sports & Classics also at one point had a stash of original mounting brackets if you're looking for those. The OEM parts fit somewhat better than the Moss repros, and the fit around the overriders (particularly if you have repro overriders and/or bumpers) can be a bit tight.

Glad you're happy w/your 576s. Nothing like a pair of big chrome fog lamps to make your car reek of British Classic. All you need now is a Harris Tweed flat-top, a pair of driving gloves, and a nice steady grey drizzle.
Mark Lambert

Hey Mark, you are talking about my standard driving attire! But it's been a bit more than steady grey drizzle this year.

Steve
Steve Gyles

Mark and Steve,

You should try Tasmania, today I was out in my Harris Tweed flat cap and my driving gloves, but no grey sky. It was 14oC and the sun was shining.

Photo attached

regards,

Ken Taylor
J K Taylor

Picture now attached


J K Taylor

Mark and Ken

I forgot to mention the goggles to cut out the glare of those fog lamps!!!

Steve


Steve Gyles

Thanks for the picture Steve. I printed it out and put it on my mantlepiece - keeps the kids away from the fire!

Seriously though Ken, how do you keep your cap on? Mine begins to want to blow away at anything over 30mph. Is there a trick or am I too tall and/or with an odd shaped head?

Neil
Neil McGurk

Neil

Odd shaped heade without a doubt. Mine stays on no problems up to 80ish. That's without the goggles!

Steve
Steve Gyles

Neil

Way back in the 60's my sister gave me a very similar cap that would stay on under all driving conditions. The "vertical" section was a knit material that stretched a bit and was "deep" enough to cover your ears in cold weather. The "extra" material folded up out of sight when you didn't need to cover your ears. Would love to find another like it since I finally wore a hole completely through the top. Maybe you can find one like it. If so let me know where I can get one.

Larry
49YT (since 1961)
58A
Larry Hallanger

hi, Ken

i put the picture here http://mg-owners-gallery.eu/
i hope you don't mind
serge

Neil,

I'm 180cms (tad under 6 foot), pull the cap down slightly at the front and it's A ok.

regards,

Ken

PS Thanks for the reply on the spare wheel cover
Ken Taylor

Thanks Ken, I'm 184cm, (although I tend to slouch!) so either it's that extra inch or so of exposed cap over the windscreen, or it's my odd shaped head. Maybe I should try Cam's body shop in Southport, maybe they could do a bit of panel bashing on my skull.

I tried a tighter fitting cap but got a headache and a big red line across my forehead. If all else fails I could go for elastic under the chin.

This would work (Gordon, is that you?) but it's a bit conspicuous when doing the weekly shop in Sainsburys.

Neil


Neil McGurk

Neil

Overall height is not the critical measurement, it's your sitting height. You may be one of those people with shortish legs and a long body. My fellow MGA enthusiast is one such misshapen human! He is only my height (175cm) but his long torso puts his head significantly high up relative to the winscreen top.

As an aside, I had to be measured to fit the Lightning jet fighter; the thigh to knee measurement when sitting was most critical. Fractionally too long and you would lose your knee caps on the front canopy strut if you ejected!

Steve
Steve Gyles

Hi All, What happened to the "wind in the hair" motoring? I only tend to wear head gear when it is bright sunshine and I need a baseball cap with a long peak to act as a sunvisor. If the wind blows my hair out - so be it. Neil, never mind panel beating your head - just take out the seat cusion and sit on the floor!! Perhaps I have the advantage in only being 5'8" albeit with short legs - would I have fitted perfectly into a Lightning Steve? Never had to eject from the MGA yet although when the brakes failed I nearly felt like it. I agree with Neil - Steve's photo was very scary indeed. Back to the thread - I have a few Lucas spot and fog lamps in pieces waiting for reassembly to make 2 good ones - Gary - thanks for the instructions in positioning the relay. Cheers Cam
Cam Cunningham

This thread was discussed between 14/08/2007 and 25/08/2007

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