Discovery dipped lights will not switch off. Help please.

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The dim-dip systems were not intended for daytime use as Daylight Running Lamps DRLs. Rather, they operated if the engine was running and the driver switched on the parking lamps (called "sidelights" in the UK). Dim-dip was intended to provide a night time "town beam" with intensity between that of the parking lamps commonly used at the time by British drivers in city traffic after dark, and dipped (low) beams; the former were considered insufficiently intense to provide improved conspicuity in conditions requiring it, while the latter were considered too glaring for safe use in built-up areas. The UK was the only country to require such dim-dip systems, though vehicles so equipped were sold in other Commonwealth countries with left-hand traffic.

In 1988, the European Commission successfully prosecuted the UK government in the European Court of Justice, arguing that the UK requirement for dim-dip was illegal under EC directives prohibiting member states from enacting vehicle lighting requirements not contained in pan-European EC directives. As a result, the UK requirement for dim-dip was quashed.

Nevertheless, dim-dip systems remain permitted, and while such systems are not presently as common as they once were, dim-dip functionality was fitted on many new cars well into the 1990s.

I was pretty close i think!

go me

Mr Noisy said:

Thanks TMM for your appreciation, allow me to explain!

Actually chaps, they should be called position lights. They are for use when you want/need to display the vehicles position on the road without actually needing lighting to see with.

When the disco was made, it was decided that the position lights alone were not sufficiently bright enough to make the car stand out in low light conditions, so a dim-dip system was fitted.

This system illuminates the dipped beam lamps to something like 1/4 brightness when the position lamps are switched on and the engine is running.

Thus, if the vehicle is parked, only the position lights are used. If the vehicle is driving, the dipped beams are illuminated dimly also, for more visibility on the road (not to see with)

TMM, you will notice that switching to dipped beam on the stalk significantly brightens the dipped beam lamps when the engine is running (obviously when your dim dip is working properly!)

For some reason it is no longer a requirement for certain cars to have a dim dip function, so it is not necessary for it to be working anymore.

If mine stopped working i would replace the relay because i quite like the old fashioned quirks about the car.

Hope that helps!

Cheers, Sam.

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Exellent Explanation Mr Noisy :clap2:

I read this thread with interest because my 300 tdi 1997 disco has developed the same prob, I have fitted a new dim dip resistor and finally as suggested unplugged the dim dip resistor but my lights are still on. It does seem to only happen when we get rain am I to assume the dim dip relay is at fault and if I take it out will my car still work.
Sorry for the stupid questions but I'm new to this forum game!

dim dip unit at a guess and it has been covered many many times

discool said:

There's no relays in a disco1 lighting circuit, the dim-dip is a seperate function and is part of the side light circuit.
If you have the later dim-dip system just pull the plug from the resistor to disconnect the system as it not required now, it's located on the engine bulkhead by the washer bottle

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I pulled out my plug but lights still on how can that be???

nokiakid said:

I pulled out my plug but lights still on how can that be???

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Pull the plugs at you light switch if they then go out u have a faulty switch otherwise it's out a multimeter and find where the supply is coming from.

Thanks for that I will have a try tomorrow.

When I got the interior of a disco **** wet through (ok I was stood inside jetwashing the headlining/dashboard etc!) the lights would not turn off til the switch dried out, so I'd guess this will be your switch too.

Give it a good wiggle/twist on and off to see if it will self-recover...

Mr Noisy said:

When I got the interior of a disco **** wet through (ok I was stood inside jetwashing the headlining/dashboard etc!) the lights would not turn off til the switch dried out, so I'd guess this will be your switch too.

Give it a good wiggle/twist on and off to see if it will self-recover...

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Thanks for that I will have a good look today, can someone please confirm the location of the dim dip unit/ relay on the disco TDI 300 1997 model.

nokiakid said:

Thanks for that I will have a good look today, can someone please confirm the location of the dim dip unit/ relay on the disco TDI 300 1997 model.

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The dim-dip relay has yellow cable markers and can be located on the hinged relay bracket behind the passengers kick panel, it's just a standard relay YWB10027L. The resistor is on the bulkhead in the engine bay.

discool said:

The dim-dip relay has yellow cable markers and can be located on the hinged relay bracket behind the passengers kick panel, it's just a standard relay YWB10027L. The resistor is on the bulkhead in the engine bay.

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Thanks a lot will try and get it found before it dries out again.

nokiakid said:

Thanks for that I will have a good look today, can someone please confirm the location of the dim dip unit/ relay on the disco TDI 300 1997 model.

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See - http://www.landyzone.co.uk/lz/f8/unknown-relay-161861.html

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Thanks a lot for all your help I took the relay out and hey presto no more lights coming on every time it rains. One thing to note from me is that by taking the dim dip resistor out of circuit it did not stop the lights coming on.

Taking the dim dip resistor out of the circuit will disconnect the dim-dip function with the lighting, but if you have a short circuit/faulty componant somewhere in the lighting or dim-dip circuit then it would probably not stop your lights being permantly on, so if removing the relay has resolved the problem well done. Did you try a replacment relay?

I have just had this problem arise. I have a 1997 300 TDi discovery and the sidelights are on all the time.

I have taken the switch/steering column apart, I have taken all the fuses out. and I have just removed the dim dip relay. They are still staying on.

Has anyone got any other ideas? I tried wiggling the loom on either side but that didn't even give a flicker.

I am lost now. The only way I can get the lights out is to remove the large 30A fuse out of the engine compartment fuses.

I had this problem on an old Disco, and found it was a problem with the indicator relay of all things. Why the indicator relay would cause this was a complete mystery to me.

at a guess the loom has rubbed through to perm live-most likely wiper park feed- try round rear door as it may have broken there with movement.

Whereabouts is the indicator relay?

The haynes manual says "Passenger compartment fuse box" Is that the main one under the steering wheel?

MC1 said:

Whereabouts is the indicator relay?

The haynes manual says "Passenger compartment fuse box" Is that the main one under the steering wheel?

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Yes, it was under the steering column, it was marked flasher unit on the outside. If I remember correctly, it was a bit of a bugger to spot.