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Hi folks, I thought you might be entertained by an odd fault I fond today.

I was approached in the supermarket by a man I know who was having electrical problems with a 1978 Datsun 180B (610 for the aficionados). he had owned it for the better part of two years, but had never been able to get the high beams working; it seemed to have only dipped beams, no matter what the position of the flasher switch. The 180B has four 5" lamps, the inners being high beam only and the outers being dual filament.

I could clearly hear the relay clicking, but the lights didn't change. This is a simplified diagram of the circuit with only one side shown:

Lighting Circuit.JPG

The flasher switch operates the headlamp relay, but it's a little odd in that in the default dipped beam position the relay is powered. Pushing the stalk forwards (or pulling it back to the 'flash' position) will remove power from the relay coil, causing it to change state. All of the switches were working correctly, but the relay output wouldn't change. You can see the headlamp relay arrowed:

Relay with arrow.jpg

Eventually I pulled the relay and opened it by prising back the dimples in the case, and this is what I found:

Relay 4 annotated.jpg


It's a little hard to see, but the relay moving contact wasn't touching either of the fixed contacts. The coil was pulling in mechanically, but electrically nothing was happening. If you look back at the first photo, you can see a small Philips screw to the left of the arrow. It seems someone turned this screw.

So why were the lights working at all? The screw had been turned clockwise and this rotated the frame of the relay until it lodged against the dipped beam contact. It was a fluke that the headlights worked at all, it was the accidental short circuit that kept them on.

The main beam contact surface was pretty poor, so I advised the owner to track down a NOS relay.

That took me at least 20 minutes. I'm getting slow in my old age :)
 
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static zap

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Advent Win
Bears a strange similarity to a Ford Estate I had , with a insidious battery drain ,
and a warm relay with ignition off !
... Dim dip circuits get even more perplexing (1 headlight classics ?) ...
 
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