Disco 1 Headlight switch functions

Georgeblade · Oct 26, 2022

Hello,

My 1993 pre-facelift is confusing me.
With the ignition OFF and the lights set to Sidelights it seems I have only the small sidelight bulbs illuminated which I think is correct.

When I start up, with the switch still in the Sidelight position the headlights come on Dipped but not fully bright compared to when the switch is actually in the Hedlights position.

Pushing the switch to headlight position the headlights are fully Dipped.

Full Beam works as it should.

Has anyone come cross this, or is it working as it should?

Many thanks for any help on this one.

Stanleysteamer · Oct 26, 2022

My Disco 1s are not as old as yours. I think you'll find the 1st case is parking lights, the second case is sidelights and the third is dipped beam.
don't worry about it!

Look at the number plate bulbs in the first two cases. I think you'll find in case one they are not on but in the second they are. At least while you are driving.
All this may be in the handbook.
Just remember you need parking lights if parked on a road at night that has a speed limit of more than 30 mph.
Don't think a Disco one of this era had running lights.

Kev12 · Oct 26, 2022

Working as intended, its called dim dip

Georgeblade · Oct 26, 2022

Stanleysteamer said:
My Disco 1s are not as old as yours. I think you'll find the 1st case is parking lights, the second case is sidelights and the third is dipped beam.
don't worry about it!
Look at the number plate bulbs in the first two cases. I think you'll find in case one they are not on but in the second they are. At least while you are driving.
All this may be in the handbook.
Just remember you need parking lights if parked on a road at night that has a speed limit of more than 30 mph.
Don't think a Disco one of this era had running lights.

Many thanks for replying.
Just checked the number plate lights as you suggested - they are on when the sidelights are on whether ignition is on or off.
According to the Paynes Manual wiring diagram for a pre 93 car the first (middle if the stalk switch) position should be sidelights and number plate lights only.

The wiring diagram also has a DIP/DIM unit connected to the oil pressure W/L and the oil pressure switch - all looks a bit odd to me.

So, I wonder what the DIP/DIM unit actually looks like and where it is?

Georgeblade · Oct 26, 2022

Kev12 said:
Working as intended, its called dim dip

So, excuse my ignorance - could you tell me where the DIM/DIP unit is and what it looks like please?
Its a relief that the lights are working as intended.

Many thanks

sierrafery · Oct 26, 2022

Be happy that it works as it should cos the dim/dip unit on early D1s is a frigging expensive thing, google out PRC8123 images to see how it looks maybe you can figure out where it is

Georgeblade · Oct 26, 2022

sierrafery said:
Be happy that it works as it should cos the dim/dip unit on early D1s is a frigging expensive thing, google out PRC8123 images to see how it looks maybe you can figure out where it is

Many thanks.

Georgeblade · Oct 26, 2022

Georgeblade said:
Many thanks.

Yikes, just looked at the price of these things.

discool · Oct 26, 2022

Georgeblade said:
Hello,

My 1993 pre-facelift is confusing me.
With the ignition OFF and the lights set to Sidelights it seems I have only the small sidelight bulbs illuminated which I think is correct.

When I start up, with the switch still in the Sidelight position the headlights come on Dipped but not fully bright compared to when the switch is actually in the Hedlights position.

Pushing the switch to headlight position the headlights are fully Dipped.

Full Beam works as it should.

Has anyone come cross this, or is it working as it should?

Many thanks for any help on this one.

+1… It is working as it should.

Its not a legal requirement so u can isolate it if you wish.
The 1995MY onwards D1 had a similar system.
Now simply unplugging the dim-dip resistor will isolate the system which I did when I started using LEDs as side light bulbs maybe 20 years ago, the reason was the bright white light of the LED looked a bit naff with the dimmed headlamp bulb so not an issue for me now.

FlyingPete · Aug 30, 2023

The connection to the oil pressure switch is a relatively crude way of switching the dim-dip based on the engine running. Normal operation will be sidelights and tail lights only when the engine is off, dipped beam at reduced intensity when the engine is running. Some systems use a resistor to drop the voltage, others use a big square voltage regulator. The latter is prone to failing- on my 90 it left the headlights on full brightness.

It's no longer a requirement, so if it's playing up, the voltage regulator can simply be disconnected to revert to a normal headlight function, the resistor type requires the relay to be removed and a couple of pins to be bridged together. Or you can disconnect the resistor but that still relies on the relay to operational.

Disco 1 Headlight switch functions

Georgeblade

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Stanleysteamer

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Kev12

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Georgeblade

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Georgeblade

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sierrafery

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Georgeblade

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Georgeblade

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discool

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FlyingPete

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