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db18 headlight / dip-switch

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Db n j
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db18 headlight / dip-switch

Post by Db n j »

So, finally got to try to resolve an issue with The Duke headlights. They have stopped working, but were eratic when last used (when I pressed the dip-switch the light went dim and the engine started to slow). I suspected the Dip-switch, but its not really a one-man job to change, as the fixing bolts are on the engine bay side of the bulkhead.

Today, I had an extra pair of hands (and another brain), so did some chasing of the wires bulbs etc. The headlight is not simple to remove, but checking and testing suggests that the wiring and bulb were ok.

The headlights works on one filament, but when the dip-switch is pressed the light either goes off or both filaments light.

To eliminate the switch, another was substituted, but behaves same.

Back to basics = if you take the Live Feed (Blue) and touch the BlueGreen wire headlight lights, do same to Blue Yellow and the other filament lights.

Try running though the switch and the light works on one terminal but when switched doesnt switch to the other terminal.

Anyone explain how the dip-switch is supposed to operate and what to check and test next.

Many thanks

Brian-H
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Re: db18 headlight / dip-switch

Post by Brian-H »

Going by those colour codes it's similar to the Consort - (the diagram below is a db18.org link)


The dip switch is simply a single pole double throw (SPDT)
i.e. one input (SP) and 2 outputs (DT)
https://www.miwv.com/wp-content/uploads ... switch.jpg

While it's by no means impossible for one of the switch contacts to fail either intermittently or completely, the problem is far more likely to be down to intermittent earth problems on one or both headlight(s) - either the earth point on the headlight body itself, or the car chassis earth point for the headlight.

Best thing to do is to take a wire direct from battery earth terminal, to the earth point on the headlight body, and also do the same for the other headlight - then test again.


EDIT - one scenario as follows

Locate the dip switch in the diagram (on the left, a bit above the tail lamps) and imagine it's set as in the diagram.

If the earth connection is absent on the right-hand lamp, then the current will flow from the dip switch, down through the 3rd fuse from the left, down to joint "4" just above the right-hand headlight, through "main" filament in right-hand headlight to the headlight body, earth not there so it continues from headlight body back into "dip" filament, up to joint "2" (left of joint "4"), across to joint "2" just above the left-hand headlight, into the "dip" filament in the left-hand headlight, then to the headlight body, then to earth. Meanwhile you'll also get current flowing from joint "4" just above the right-hand headlight to joint "4" just above the left-hand headlight, through the "main" filament in left-hand headlight to the headlight body, then to earth.

Result would be a bright light in the left-hand headlight, and 3 other filaments all connected in series, which would all glow dimly.

Other scenarios
  • no earths = no lights at all
  • earth connection absent on the left-hand lamp = opposite of earth connection absent on the right-hand lamp
  • earth connection not absent but presenting some resistance = as before with 1 bright filament but varying brightnesses in other 3 filaments (depends on the amount of resistance to earth)
  • both earth connections presenting some resistance = varying brightnesses in all four filaments
  • other possibilities also exist, depending on earths to sidelights

HenryC
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Re: db18 headlight / dip-switch

Post by HenryC »

As Brian suggests, I would check the earth connections and then the bullet connectors on the supply to the headlights. Is it a floor mounted switch?

I am a bit surprised by your comment that the engine slows. The battery should be able to supply enough power for the headlights and at idle the voltage regulator should be controlling the load on the dynamo, i.e. there should be no load on the dynamo/engine. Is the battery in good condition?
Cheers, Henry Curwen
Registrar for Conquest & Century Saloons (DJ250/1, DJ256/7, DJ260/1)

Conquest (Drop Head) Coupe DJ252

Db n j
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Re: db18 headlight / dip-switch

Post by Db n j »

Thanks for the feedback. On reflection, poor earth is a likely explanation.

It’s a b****r to remove the headlights ( the rim bolts through the wing which is covered by the stone guard, )

I removed one headlight, so now I’ll have to do the other.

The harness is (relatively ) new, and on the drivers side I can’t find any damage,

Try again later

Db n j
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Re: db18 headlight / dip-switch

Post by Db n j »

Just an update..

I had some free time, so removed both headlights. I did notice the pass headlight gave off some dust when I removed the Earth, which might suggest a
'poor connection.

I ran a wire from both lights to the earth on the battery. Headlights worked only on one filament, even when the dip was activated.

A voltage check at the switch suggested the activation did not switch to the second path.

I tired connecting the Live and the alternate wires to the bulb separately and the connection was made / bulbs lit.

I tried another device which finally switched when activated (ie original and another were therefore u/s.)

All tidied and carpet replaced etc.

On with the next job !

Brian-H
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Re: db18 headlight / dip-switch

Post by Brian-H »

So it was a dodgy switch and dodgy earth(s). Well done on sorting it :)

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