"Dave Plowman (News)" wrote in news: snipped-for-privacy@davenoise.co.uk:
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 contact, yes?
JD
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, yes.
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.
Chris
Dunno.
Not if there is a relay for the headlights somewhere. It would be the dip switch that then handles the full current.
Chris Whelan wrote in news:LCg9y.489322$ snipped-for-privacy@fx33.am:
Hi Chris, I was looking at the under-bonnet relay that is dlightly to thr nearside of center (not the one in your link)
I pullod out all of the six relays in the box shown in your link but none had any effect on the low-beam bulb that is working properly, NB There are fewer relays in that box than shown in your link.
Okay - thanks. I'm tempted to just brdge the two positive sides of the two low-beam fuses, so that power gets to the currently-dead low-beam bulb, via it's own normal fuse.
JD
"Dave Plowman (News)" wrote in news: snipped-for-privacy@davenoise.co.uk:
I cannot find a relay for the low beam bulbs at all. I just made a new discovery though: the positive side of the low-beam fuse sockets are live, even when the lights are switched off. I guess this means the power from the battery goes directly to the fuse box, and then after going through a fuse, the feed goes to the headlight switch before going on to the light bulb. This means it could be the headlight switch that's caput, doesn't it? That's assuming that there is two separate contacts inside the headlight switch - one for each bulb. If there is only one contact, then the break in the circuit must be elsewhere.
JD
Chris Whelan wrote in news:LCg9y.489322$ snipped-for-privacy@fx33.am:
I just found out the positive side of the low-beam fuse sockets are live, even when the lights are switched off. I guess this means the power from the battery goes directly to the fuse box, and then after going through the fuse, the feed must go to the headlight switch before going on to the light bulb. This means the headlight switch may be at fault doesn't it? To me that seems more likely than a break in the wiring, don't you agree?
That's assuming that there is two separate contacts inside the headlight switch - one for each bulb. Is that likely? If there is only one contact, then the break in the circuit must be elsewhere.
JD
How does this reconcile with "What I have now discovered is that there is no voltage between one side of the fuse socket and the other"?
Are you able to see my posts?
I ask because you have already been told that if you have no daytime running lights, then there are no relays for the headlights.
I would be amazed if any car maker would provide separate contacts, which would also mean extra wiring, for each individual bulb.
If you are *sure* the bulb is OK, and you are *sure* there is no voltage reaching the bulb, in the absence of a wiring diagram your only option is to physically trace the loom back to wherever it connects to, and test there.
Chris
Here, see if this helps. You need diagram 4:
Note - it will only be there for one week!
Chris
Fredxxx wrote in news:n4f5sf$2to$ snipped-for-privacy@dont-email.me:
I don't know. I find car circuitry hard to fathom.
JD
Chris Whelan wrote in news:vlFay.633759$ snipped-for-privacy@fx33.am:
Thats very helpful - thank you! The colour makes it a lot easier to understand. I'm thinking that it would proably be a more sensible gamble to simply replace the headlight switch and see if that cures it. If not then I really will have to track down a broken wire, but I think you'll agree a break in a wire is a bit unlikely, isn't it?
JD
If you are using a digital meter the voltage you are seeing may not be 'power' as such, but a back feed from another circuit. See if the 'power' you are seeing will actually light a bulb.
]]
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?
JD
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!
Peter
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?
JD
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.
Peter
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