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Re: VB's Heavy Duty Headlamp upgrade - A WARNING!

To: "Jack Feldman" <>, <>
Subject: Re: VB's Heavy Duty Headlamp upgrade - A WARNING!
From: "Paul Hunt" <>
Date: Fri, 10 Mar 2006 15:56:40 -0000
Firstly any fuse *or* circuit breaker that cuts power to both headlights on
both beams should only ever be used if there are also individual filament
fuses/circuit breakers.  And 2nd circuit-breakers aren't always
self-resetting.  And even if you *do* have self-resetting circuit-breakers
depending on where the short has occurred and how bad it is you still may
not get any light output in the event of a short.

If fitting uprated headlights it is *essential* that you fit relays (plural)
so that the original manual switch doesn't have to carry any extra current.
Whether you fit fuse/circuit-breakers is a separate decision, but given the
current carrying capacity of relay systems any unprotected wiring will
suffer major damage in the event of a short, more so than the original,
where the main lighting switch is a weak link if nothing else.  With one
fuse/circuit breaker per filament i.e. four in total, at about double the
rating of the filament current requirement, if the fault occurs on a
filament wire only one headlamp on one beam will be affected.  The wiring
between individual fuses and relays should be kept as short as possible -
like no more than a couple of inches - which only leaves the main wiring
between relays and main power source e.g. solenoid unprotected.  You can add
a fifth fuse or circuit breaker which should be at least double that of the
individual filament items, but if you do a decent job of wiring you should
end up with a much shorter run and hence much less likelihood of shorting
out than original wiring.  If a major short occurs here - which should be
*less* likely than on the original wiring - then you aren't going to get any
light from the headlamps anyway.  Fused you will lose all lights but protect
the wiring, unfused you will lose all lights and do major damage to the
wiring, it seems a 'no-brainer'.  With a partial short you could well have
some glow from the lights and still do no damage if you act promptly i.e.
stop and switch off.  That does leave the intermediate situation where a
short may be bad enough to blow a fuse if fitted, but give some residual
light if not, but like I say if you do a proper job of the solenoid to relay
to fuse wiring the chances of shorting out will be negligible.


----- Original Message ----- 
> Two problems: one, there are no fuses in
> the harness and two, never fuse your headlights. Circuit breakers are what
> should go in the headlamp circuit. That way when there is a short the
> gives you light from time to time, and you are not stranded in the dark.

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