that would put double the load on the existing working fuse and wiring,
the relay is designed to power both, so that will be ok. I would try it
using the existing rating of fuse, if that survives then it will be ok
for a while at least.
Both fuses themnselves are faultless and intact. The problem is no power to
the fuse (in the case of the light that doesn't come on). As for a relay, I
cannot find one that has ane effect on the headlight that does work. Is it
certain that there IS one for the low beam, do you think?
Did you look at the link I posted earlier? It clearly lists two headlamp
relays, with a diagram showing their location.
There will be one relay for dip, and one for main. It's possible that there
are separate contacts on each relay for LH and RH side, in which case the
fault might be the dip relay.
It's more likely that there is a single contact feeding one wire to the fuse
box, which then splits within the base of the box. In that case the fault is
likely to be a break under the fuse box.
This seems to be my best option. I am thinking of making up a lead with a
crocodile clip at one end, which I clip to the battery positive, then feed that
wire to a new dashboard auxiliary switch and have another wire going from this
switch to the headlight. Is a fuse really necessary for this?
Yes a fuse is essential, use an in line one close to your crocodile
clip, not that I approve of your method of connecting to the battery.
Without a fuse you run the risk of a few meters of glowing red hot wire
- been there and done it, albeit 50 years ago!
I agree about the crocodile clip; I securely clamped the wire instead.
Surely, the bulb itself will act as a fuse, won't it? I couldn't find an inline
fuse today, so I wired it up with no fuse. Why would the wire get red hot?
Are you a mechanical superhero, incapable of making mistakes?
If so, leave the fuse out.
If you're a normal human being, put one in, because that way when you
accidentally short the wire onto something (not entirely unlikely) the
fuse will blow rather than you ending up with a red hot wire dripping
insulation all over your nice engine bay.
A fuse is the 'weak link' in a circuit, it's purpose is to protect the
wiring in the event of a fault. For example, in your case, if you have
an accident and your headlamp assembly is badly damaged such that the
wiring is crushed against the body shell there is a real possibility
that the battery will supply as much current as it can down the damaged
wire which will result in it becoming very (red) hot and melting the
insulation and that of the adjoining cables ultimately catching fire.
The purpose of the fuse, located relatively close to the battery, is to
fail if an excessive amount of current flows therefore stopping further
current flowing and reducing the chance of fire. Please for your own
and your passengers safety fit a fuse, it's not funny being in a car
that catches fire it does very, very quickly become an inferno. Most car
fires are a total loss.
I posted the Hayens schematic here:
Can anyone decipher that and tell me what the relay should look like?
BTW, I'm puzzled by that schematic, because it doesn't show any single-
filament headlights. My low beam lights are separate, single-filament
Haynes manuals are not even very useful as a door stop, let alone a
reference. If I had the time and was paid to do it, I would visit them
and point out some of the errors I have noticed from the distant past
when I used to refer to them.
The car has no daytime running lights. There is a relay labeled "main"
being an 80A relay. Would that mean 'main beam'?
If there is no relay for the low beam bulbs, this means that the full
current for both low-beam bulbs goes through a single headlight switch
Where are you looking at? There is a relay labelled 'Main' in the fascia
relay box that feeds various 'ignition on' circuits; it will have nothing to
do with the lights.
There are either one or two under-bonnet relay boxes shown in the link I
posted. The smaller one of the two holds the headlight relays, but may not
be fitted to your vehicle.
If your vehicle has only one under-bonnet relay box, then that is the case,
Whichever arrangement you have, if your fault is with the dip beam in one
headlight, the problem can only be at or after the fuse box, because
everything before that is a single circuit.
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