Nearside Headlight Blowing Fuse

Al2O3 · Oct 4, 2021

I know there's a good chance that is is going to be an earth issue, but I don't know where.
Initially, I thought this was a fault with my boomslang harness. The boomsland has two relays and one of the terminals over heated distorting the holder. I replaced the two relay holders and made sure the terminals on the relays were clean. The nearside headlight 7.5A fuse had blown and I didn't have a spare of that size, so I ordered some. Now that they've arrived I've discovered it's blowing the fuse as soon as I put the headlights on. I disconnected the boomslang and reconnected the two original Land Rover plugs on to the headlights. It still blows the nearside fuse, so it doesn't seem to be the boomslang. I've not had the engine on and the lights have only been on for moments at a time, but I pulled the Land Rover headlight relay out from the fuse board and it felt warm. No idea if this is ok or not? i.e. should it get a bit warm?
Any ideas where I can look for a fault with the nearside headlight? Cheers.

v8250 · Oct 4, 2021

This sounds like a knackered wiring issue causing high load to the relay, hence warm. I'd relocate a new earth with new earth wiring and check original headlight wires from fuse output, via switch to the interconnect with the new Boomslang wiring.

When I replaced my under bonnet wiring most of the looms/wires looked in good condition. It was when I remover the tape insulation I found birds nests of aged/brittle wiring and PO bodges. The only answer was to rip out the whole lot and wire in new.

Al2O3 · Oct 4, 2021

v8250 said:
This sounds like a knackered wiring issue causing high load to the relay, hence warm. I'd relocate a new earth with new earth wiring and check original headlight wires from fuse output, via switch to the interconnect with the new Boomslang wiring.

When I replaced my under bonnet wiring most of the looms/wires looked in good condition. It was when I remover the tape insulation I found birds nests of aged/brittle wiring and PO bodges. The only answer was to rip out the whole lot and wire in new.

I've just been out for another look because a bit of Googling brought up another LZ thread with the same problem. Someone suggested trying it without the headlight connected, to rule the headlight unit out. Just tried that and fuse was fine. Swapped the bulb for a new one and worked fine

fuse ok.
What I've noticed now though is that when I put the switch to side lights the headlights dont come on via the dim dip relay. Pretty sure they did before

I'll check in the handbook.
So, fuses not blowing for now, but I suppose I might have moved the wiring and temporarily cured the short.

EDIT
I've checked the hand book and the headlights should be coming on via the dim dip

mick 1986 · Oct 4, 2021

Al2O3 said:
I've just been out for another look because a bit of Googling brought up another LZ thread with the same problem. Someone suggested trying it without the headlight connected, to rule the headlight unit out. Just tried that and fuse was fine. Swapped the bulb for a new one and worked fine fuse ok.
What I've noticed now though is that when I put the switch to side lights the headlights dont come on via the dim dip relay. Pretty sure they did before I'll check in the handbook.
So, fuses not blowing for now, but I suppose I might have moved the wiring and temporarily cured the short.

EDIT
I've checked the hand book and the headlights should be coming on via the dim dip

The dim/dip will probably be a large enough current to energise the relay in the boomslang harness and make them come on as normal. Is that what you mean was happening, and now isn’t?

The fault probably isn’t an Earth fault. If you imagine the circuit in a really simplified form, it has power, switch, load, and Earth/return. If you short the Earth/return line back to the Earth, then it’s exactly the same circuit. If you have a live shorting to Earth, or a bad/dirty connection, that will cause a current spike, the relay will heat up, and the fuse should blow. I was going to suggest trying it without the headlight fitted, but as that has been tried and is working, I’m not sure where to start. Maybe check the wiring along the inner wing?

Al2O3 · Oct 4, 2021

mick 1986 said:
The dim/dip will probably be a large enough current to energise the relay in the boomslang harness and make them come on as normal. Is that what you mean was happening, and now isn’t?

The fault probably isn’t an Earth fault. If you imagine the circuit in a really simplified form, it has power, switch, load, and Earth/return. If you short the Earth/return line back to the Earth, then it’s exactly the same circuit. If you have a live shorting to Earth, or a bad/dirty connection, that will cause a current spike, the relay will heat up, and the fuse should blow. I was going to suggest trying it without the headlight fitted, but as that has been tried and is working, I’m not sure where to start. Maybe check the wiring along the inner wing?

When I was sorting the boomslang relays last weekend I noticed that when the sidelights were put on the headlights came on full. When I took the boomslang out and went back to standard set up the headlights came on dimly when the switch was put to sidelights. I'm back to standard set up again and only the little indicator sized side lights come on when the switch is in the sidelight position. The dimmed headlight feature no longer works.
And as I was typing this the alarm has just gone off on it. It's never done that before!

Yes, I don't think it's a bad earth I think it's a short somewhere. I think you're right, checking the wiring along the inner wing may be the answer

mick 1986 · Oct 4, 2021

Al2O3 said:
When I was sorting the boomslang relays last weekend I noticed that when the sidelights were put on the headlights came on full. When I took the boomslang out and went back to standard set up the headlights came on dimly when the switch was put to sidelights. I'm back to standard set up again and only the little indicator sized side lights come on when the switch is in the sidelight position. The dimmed headlight feature no longer works.
And as I was typing this the alarm has just gone off on it. It's never done that before!

Yes, I don't think it's a bad earth I think it's a short somewhere. I think you're right, checking the wiring along the inner wing may be the answer

If the dim/dip is a function you want to keep, then look at replacing the relay. I don’t think it’s that expensive, but I didn’t really look as I disabled mine.

Yes I think a short is the answer, but finding it might be a little tricky. The wing is the easiest place to start with. Just thinking there, where does the feed split? Does it split at the headlight switch, I think it does. If that’s the case, it could be anywhere on that wire.

Al2O3 · Oct 4, 2021

mick 1986 said:
If the dim/dip is a function you want to keep, then look at replacing the relay. I don’t think it’s that expensive, but I didn’t really look as I disabled mine.

Yes I think a short is the answer, but finding it might be a little tricky. The wing is the easiest place to start with. Just thinking there, where does the feed split? Does it split at the headlight switch, I think it does. If that’s the case, it could be anywhere on that wire.

Do you think the dim/dip stopping is because the relay has carped?
I've no idea where the feed splits. It's going to be a fairly steep learning curve Mick

mick 1986 · Oct 5, 2021

Al2O3 said:
Do you think the dim/dip stopping is because the relay has carped?
I've no idea where the feed splits. It's going to be a fairly steep learning curve Mick

I would guess it is, but you won’t know without testing it to be honest. The resistor that causes the headlights to be dim could also be an issue. Mine was located on the drivers side inner wing, I’m not sure if yours is in the same location.

Don’t worry about the learning curve, there are plenty people on here who know enough about electrics to help you get it sorted.

Hicap phill · Oct 5, 2021

I don’t think the problem is the lights as the thought the boomslang loom removes the fuses used normally.
You have a fused live to the boomslang & the relays switch the relays for high/low beam.
Only fused which would therefore be used is the side lights.

mom with @mick 1986 & the dim/dip causing the problems

mick 1986 · Oct 5, 2021

Hicap phill said:
I don’t think the problem is the lights as the thought the boomslang loom removes the fuses used normally.
You have a fused live to the boomslang & the relays switch the relays for high/low beam.
Only fused which would therefore be used is the side lights.

mom with @mick 1986 & the dim/dip causing the problems

I thought the boomslang plugged into one of the original light plugs, and used them feeds as a trigger for the new relays, with power feeds direct from the battery?

Hicap phill · Oct 5, 2021

mick 1986 said:
I thought the boomslang plugged into one of the original light plugs, and used them feeds as a trigger for the new relays, with power feeds direct from the battery?

Yes you are correct….
So wonder if you swap the boomslang switch wire ,would it blow that fuse & mean problems else where?

(My switch wires have been change for stalk & separate carling switch.)

mick 1986 · Oct 5, 2021

Hicap phill said:
Yes you are correct….
So wonder if you swap the boomslang switch wire ,would it blow that fuse & mean problems else where?

(My switch wires have been change for stalk & separate carling switch.)

That was the way I was thinking, remove the bulb, then swap the feed over to the other side.
Mine is still switched through the stalk, but all 4 lights have their own relay now. It’s a bit overkill, but I have bright lights, and a fairly reliable system.

Al2O3 · Oct 5, 2021

mick 1986 said:
I thought the boomslang plugged into one of the original light plugs, and used them feeds as a trigger for the new relays, with power feeds direct from the battery?

Hicap phill said:
Yes you are correct….
So wonder if you swap the boomslang switch wire ,would it blow that fuse & mean problems else where?

(My switch wires have been change for stalk & separate carling switch.)

Yes, it does. And my left hand headlight plug, plugs in to the boomslang to trigger it. Looks like the fault (short or whatever) is in this headlight feed. It has occurred to me that I could swap the boomslang over. It probably won't be too much hassle, but I will need to extend the live and neutral wires so that they can reach the battery again.

mick 1986 · Oct 6, 2021

Al2O3 said:
Yes, it does. And my left hand headlight plug, plugs in to the boomslang to trigger it. Looks like the fault (short or whatever) is in this headlight feed. It has occurred to me that I could swap the boomslang over. It probably won't be too much hassle, but I will need to extend the live and neutral wires so that they can reach the battery again.

Extending the wires is an easy enough job. The fault will still be there if the headlight feed is shorted to Earth. If you have some wire handy, and a few male spade connectors, you can run a temporary trigger wire from the other side to the boomslang. If the fault doesn’t come back, then all is well and the boomslang can be modified at that point. It will be a waste of time if you move it over and the fault is still present.

Al2O3 · Oct 6, 2021

mick 1986 said:
Extending the wires is an easy enough job. The fault will still be there if the headlight feed is shorted to Earth. If you have some wire handy, and a few male spade connectors, you can run a temporary trigger wire from the other side to the boomslang. If the fault doesn’t come back, then all is well and the boomslang can be modified at that point. It will be a waste of time if you move it over and the fault is still present.

It has been crossing my mind about making up a harness to run from the offside across to the trigger connector on the boomslang at the nearside. The offside headlight works fine when connected to the original feed. On the faulty nearside I could leave the fuse out and then the short won't be a problem. Feels a bit of a bodge though and I should really take the inner wheel arch out and try to trace the issue. As the nights are cutting in, I'll have to do something soonish.

v8250 · Oct 6, 2021

Hi @Al2O3 , cut out old wiring and install new sleeved wiring to logical supply point near bulkhead using proper connectors.There's no need to remove wing for this and the new cable can be attached to underside lip of inner wing for super easy access. This takes no longer than a bodge [read, usual Landy owner wiring standard

], and you'll sleep all the better knowing those extra special lighting electrons are buzzing around/flowing cleanly into those H4's with minimal high resistance bodgery

Al2O3 · Oct 6, 2021

v8250 said:
Hi @Al2O3 , cut out old wiring and install new sleeved wiring to logical supply point near bulkhead using proper connectors.There's no need to remove wing for this and the new cable can be attached to underside lip of inner wing for super easy access. This takes no longer than a bodge [read, usual Landy owner wiring standard ], and you'll sleep all the better knowing those extra special lighting electrons are buzzing around/flowing cleanly into those H4's with minimal high resistance bodgery

Wasn't thinking of removing the whole wing, but that bit of harness runner under the wing is tied in with the original clips. I was expecting to get to it by taking the wheel arch liner out. I didn't mean the inner wheel arch. I think you're right, I should investigate it and cut the faulty bit out.

v8250 · Oct 6, 2021

Al2O3 said:
I should investigate it and cut the faulty bit out.

This +1, with wiring always cut out old, wire in lovely new and sleeved wires. It's amazing the amount of dead/crusty/used/fooked wires I cut out of the LR...and so many classic cars too. Spaghetti platefuls of the stuff...it amazes me why PO's are such a bunch of hamfisted bodgers with wiring. It's only simple 12VDC, the majority of which is low current/power draw...yet people cut n splice and fcuk around and always overloading ccts with overpriced heaters, daylight producing lighting bars and whopping winch guffage.

It's no wonder Land Roves self combust...

Nearside Headlight Blowing Fuse

Al2O3

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