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

To: "Dodd, Kelvin" <doddk@mossmotors.com>, <mgs@autox.team.net>
Subject: Re: [Mgs] Need info on original 1968-71 MGB fog lamp switch
From: "Paul Hunt" <paul.hunt1@blueyonder.co.uk>
Date: Tue, 7 Aug 2007 09:52:02 +0100
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.


----- Original Message ----- 
> The switch appears to work in the same manner as the headlight.
>
> Position one (top depressed) no lamps
>
> Position two (neutral center) the fog lamp is connected to the side lamp
> circuit (this can be changed to the headlamp low beam circuit where
> required by law)
>
> Position three (bottom depressed) the fog lamp is still connected to the
> side lamp circuit, the spot lamp is connected to the high beam circuit.
>
> I still think the fog lamp logo points to the right.
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