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Re: Headlamps on 79 B Roadster.....

To: "Gosling, Richard" <>, <>
Subject: Re: Headlamps on 79 B Roadster.....
From: "Paul Hunt" <>
Date: Tue, 8 Aug 2006 12:48:17 +0100
Modern practice (well, I say modern but my 89 Celica has this) have many of
the fuses mounted right by the battery (which also has one or two fusible
links right on the battery post) and feed permanent 12v out to many of the
components.  The switches then feed out a ground to power the component.
Thus if any of the 12v wiring is shorted out the fuse blows, and if any of
the switched wiring shorts out nothing worse happens than the component
operates.  Very different to 60s practice.  It also means only one fuse is
needed per headlight and not one per filament.  Paradoxically the headlamp
flasher circuit on the MGB *is* fused, off the purple circuit (always on).
So if your headlamps do fail at night you can pull on the headlamp flasher
and see to stop safely ... if you have the presence of mind!


----- Original Message ----- 
> Of course, they could have created a system which protected the circuits
> AND prevented total blackout by having a separate fuse for each
> headlamp, so if one blew you still had the other, but either
>  a) the fuses would have to have been downstream of the switch, leaving
> the switch unprotected
> Or
>  b) the fuses would have to be upstream of the switch, requiring a more
> complex switch with two separate supplies and outlets, one for each
> headlamp, as well as a supply and outlet for the side/tail/gauge lights.

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