Thank you for your quick reply. I think it might be. Either that or an old style CTEK Connextor - after I posted I had a brainwave that it might be so I have emailed CTEK support.
CTEK make adaptors to connector older style chargers to newer style “comfort connect” accessories, but I can’t find one to go the other way, ie newer charger to older accessories.
The photo in the wikipedia article isn't a very good one, because it doesn't show the ridge that the clip on the mating plug latches over, but if you look on ebay for Tamiya connectors you'll see a lot of better photos. Coincidentally I've used a pair of these connectors to make a poor man's CTEK quick connect type of lead on my W221, for a Lidl battery charger.
The photo in the wikipedia article isn't a very good one, because it doesn't show the ridge that the clip on the mating plug latches over, but if you look on ebay for Tamiya connectors you'll see a lot of better photos. Coincidentally I've used a pair of these connectors to make a poor man's CTEK quick connect type of lead on my W221, for a Lidl battery charger.
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Thank you for all of your replies, it’s much appreciated.
CTEK Support came back straight away and confirmed that it was a first generation “quick” connector, and recommended that it be replaced with a new generation CTEK Comfort connector. Now fitted, sorted