[Mgs] Need info on original 1968-71 MGB fog lamp switch

[Dodd, Kelvin]

Paul:

I don't have access to an original switch, but dissecting one of our
repros indicates that the guts are exactly the same as the headlight
switch, except that on the headlight has the power feed ganged across
terminals 3 - 4. The driving lamp switch does not giving separate feed
to the two lamp circuits. This makes sense, so I'm going with it.

In the US you are required to have headlamps on with fog lamps (which
makes absolutely no sense to me), but it's unlikely to be enforced in
most states.

I want to ensure that when we make a new production run the switch
performs as original, then the installer can wire it as they wish.
Personally if I had my way, I'd add the later 73-76 green jewel at the
top and make it so it will illuminate when on, but that's going beyond
the originality theme.



Kelvin Dodd

> -----Original Message-----
> From: Paul Hunt [mailto:paul.hunt1 at blueyonder.co.uk]
> Sent: Tuesday, August 07, 2007 1:52 AM
> To: Dodd, Kelvin; mgs at autox.team.net
> Subject: Re: [Mgs] Need info on original 1968-71 MGB fog lamp switch
>
> Logically fog lights should optionally come on with the parking
lights,
> and
> spots with the main beams.  It certainly wouldn't make sense for the
fogs
> to
> only be on with the headlights, main or dipped.
>
> The schematics show the single switch but unfortunately not the
internal
> connections,  Red (parking lights) is connected to terminal 4,
blue/white
> (main beam) to 5, blue/yellow (spot) to 1 and red/yellow (fog) to 2.
In
> drawing the light faces to the right same as for the main lighting
switch.
>
> The *toggle* switch looks like it was the earlier simple on/off switch
> hence
> one each was required for fogs and spots.  The rocker looks more like
the
> main lighting switch but they have different part numbers, and indeed
> different terminal numbers on the same schematic.  The Parts Catalogue
> quotes a quantity of 2 for both items, but that could be an error i.e.
> simply carried forward from the old item to the new.
>
> The main lighting switch is a relatively simple switch having a single
> input
> connected to nothing when off, connected to one of the output
terminals in
> the first position (i.e. parking lights), and both output terminals in
the
> second position (i.e. parking lights plus head lights).  By contrast
the
> combined fog and spot lamp switch needs two inputs - one from the
parking
> lights and one from the main beam.  In the off position neither are
> connected to anything.  In the first position the parking light input
is
> connected to the fog light output.  In the second position the main
beam
> input is connected to the spot light output.  It would make some sense
> (except for rallying) for the fog light output to be disconnected when
in
> the spot light position as both aren't usually required together for
road
> use (except by poseurs) and it reduces load on the dynamo/alternator,
but
> I
> don't know whether this was the case or not.
>
> PaulH.