Another Headlight Problem

I have a 300tdi bulkhead and loom fitted to my my '89 110. Last December I had problems with my headlights and replaced the indicator stalk with a genuine Lucas one which solved the problem (Thread).
This morning while driving to work I lost my headlights again and seem to have the same problem back. The position I am in now is:-

headlight switch:
side lights position - work as normal with side lights, tail light and dash illumination working
headlight position - no headlights, no side lights, no tail lights, no dash illumination
Main beam switch:
flash - all working as normal
main beam on - no headlights, no side lights, no tail lights, no dash illumination

I am assuming that because when flash is used the headlights are still fully functioning that the problem is going to be switch/relay/dashboard related rather than a problem with the lights themselves. I have not yet had a chance to take it apart to have a look but if any one can give me any suggestions as to what it is likely to be or specific things to check that would be great.
I am also amusing that it should not be the indicator switch again as that is less than 12 months old, however I will try and test this when I have some time.
If it turns out to be the switch again what causes them to fail? If i have another fault which is causing them to burn out? I would like to rectify root cause rather than just repairing the symptoms.

p.s looking up information on this a lot of people talk about the dim-dip relay. but i have not found a description of what this is is for or how to work out if you have one as my understanding is they were not fitted to all models. Can any one shed any light on this?

Assume nothing - it's a Land Rover. The switch is the first place to look. I'd have a really close look at the contacts to see if it has been badly made. If it looks burnt, then you have a short to earth somewhere else that is overloading the switch. It's worth checking the fuse and fuse contacts too, of course.

As above - it is most likely the switch, even the good ones are made of chocolate - the Lucas ones might be ferero rocher to the cheap ones Lidl etc....

Worth fitting the boomslang harness, or making your own to take the load off the switch - if you fit another relay into the supply to the harness switched by the "ignition" you make it so it's impossible to leave your headlights on with the engine orft

Even if the switches are cheap and poorly made what makes hem fail? If there is an underlying fault i would like to fix that to try and get a better life span out of the switch.

Disco1BFG said:

Worth fitting the boomslang harness, or making your own to take the load off the switch - if you fit another relay into the supply to the harness switched by the "ignition" you make it so it's impossible to leave your headlights on with the engine

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As I have the 300 wiring loom I already have this, unless the ignition is on it is side lights only. I also thought the 300 ones ran through relays arleady so the switch did not take much load, it has the smaller td5 style connectors on it rather than the larger bullets of the older switches.

Very similar issue with my 200TDi right now - new switch ordered Monday, hopefully once fitted will resolve. Boomslang I also have sitting in my garage - fitting is 'on the list' !

If you have a later loom with relay switched lights, you should be able to hear the relay when you move the switch. If you fitted the layer loom - did you also fit the relays?

zeaphod said:

If you have a later loom with relay switched lights, you should be able to hear the relay when you move the switch. If you fitted the layer loom - did you also fit the relays?

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I have the later loom as during the rebuild a complete 300tdi bulkhead was fitted including the complete dash and bulkhead wiring loom.

Mr S1 said:

Very similar issue with my 200TDi right now - new switch ordered Monday, hopefully once fitted will resolve. Boomslang I also have sitting in my garage - fitting is 'on the list' !

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Whta causes the switches to fail, and how do ou trace the fault if it is shorting and overloading?
I may get one of the boomslang harness to unload the switch even further as they seem to have good reviews, where does the "power" come from, is it back to the battery or taken off starter/alternator/etc

When the switch is operated a small spark is created between the contacts, this creates a little carbon, particularly in a dirty atmosphere. After a while - usually years, this carbon can build up on the contacts. As the current flows through it, it heats up, eventually melting the plastic and causing the switch to fail, or even start a small fire. The power for the aftermarket is taken off the alternator terminal. To test for a short you could remove the bulbs and test the resistance between the fuse position (fuse out) and earth. There should be a very high reading.

zeaphod said:

When the switch is operated a small spark is created between the contacts, this creates a little carbon, particularly in a dirty atmosphere

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I have just spend two and half week driving around the desert in Morocco is that likely to have caused the problem with the amount of dust in everything or am I grasping at straws?

Can you give some more details on testing the resistance. Remove the fuse and the bulbs and check fuse to earth resistance? Is that with the circuit switched on or off?

Dust and vibration on your trip may have caused the new switch to fail - or it could just need to have the contacts cleaned. I'd test the circuit with the switch in the off position first - this is testing the wiring between the fuse and the switch, then with the switch on, this is then testing the resistance to earth the whole way to the lights. You don't have to take the headlight bulbs out, it may be easier to unplug the socket at the back of the headlights.

Well having gambled and ordered the main beam switch when when i stripped it all down today it is the headlight switch that has failed. The standard "pin" sinking into the melted plastic. I managed to build it up enough to make contact with some solder so i have headlights again while i wait for the correct switch to be delivered.

Does the Boolslang harness prevent large current travelling through the headlight switch as it only turn has to relays?

Yes. But I thought you had relays install3d already as part of the 300tdi harness.

zeaphod said:

Yes. But I thought you had relays install3d already as part of the 300tdi harness.

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So did I as the headlights only come on when the ignition is one but the headlight switch has a permanent live feed so there must be relays somewhere. However the size of the cabling and the spades in the plug suggest it is taking a larger current than the equivalent wiring and spade plug on the indicator switch. I will do some more research but it is cheap enough and apparently gives slightly brighter headlights as a by product so if it is easy enough to fit I may give it a go.

Side lights dont run on relays, nor do dash lights. Lucas switches are fine and dont burn out in a year, landrover wouldnt use them if they did.

You need to overhaul your electrical system, fitting a 300 harness isnt fitting a new harness, fitting a boom what ever isnt fixing anything, clean all your connections, battery, earth, starter, bullet , light sockets, bulbs, everything.

Do you have a multimeter? How quictly does your engine turn over on the starter? What voltage are you getting at the switch then at the bulbs?