Headlight problem?
 

Just used the car for a short trip this evening, when I came back turned the headlights off when the engine was running and the ydid not go off, just dimmed. They would not go off until the ignition was turned off, strange.

Can anyone tell me what's going on please.

I'm guessing earth return fault.

Thanks for the thought, but surely there should not be any power to the headlights with the lighting switch off.

On the off-chance, I bought a spare headlamp relay, or whatever is is that is mounted on the bulkhead in the engine compartment, it's the one with cooling fins on. What does this do?

Well, sort of made a bit of progress. The problem was that headlights were on (dim) when lighting switch was off and ignition on. The only way to get the headlights off was to turn ignition off.

In the engine compartment, mounted on the bulkhead, is a relay with fins on it. I remembered that on my previous 340, over 12 years ago, I disconnected this relay because of some problems.

So, I pulled the connector off the relay, needed a little WD40 as is was very stiff.

Now the lights work correctly, ie. ignition on and lighting switch at 0, no lights.

I believe that the relay that I disconnected is the dim-dip relay.

I don't remember the dim-dip ever working on this car, the unit just gone faulty in a further way last night.

Replacement relay now ordered from ebay (£7.50), though, when it comes, I may just test it and leave it disconnected. pic. of relay attached.

Hope this is helpful to others.

yes ! the dim dip controller .. so when you turn the ignition on the headlamps come on dimly even when Turned off ., This was a law in the 1980's trying to stop people driving around with only side lights on . A nice idea so worth having working . 340's abroad do have day running lights, i have not found out how to enable that on UK models yet . anyone have a full wiring diagram book for the later models ?

I have several different version Haynes manuals, is the wiring diag. that you require likely to be in those?

Jut pulled apart the faulty dim-dip relay, photo attached!

The integrated circuit is a Decoder/Demultiplexer.

I was expecting to see corrosion or burning!

I was not expecting to see so many components. I don't have a clue as to how it works.

Most likely failure though is one of the electrolytic capacitors, about 27 years old now.

it is a Pulse Width Modulation circuit , It switches the headlamps on and off rapidly about 100 times a second , the ratio of ON to OFF is what determines the brightness , it can be adjusted slightly with the Potentiometer inside .