Thanks Hughes but so did we - the relay on the aircraft wasn't allowing the power through to the starter. it worked with the Wessex but not with the Sea King - a problem for the greenies to sort out.
IIRC from Mk2 days, you have to have 24v on the third pin of the DC external power connector in order to get the socket to accept external power. It works the other way round too, so where you could run a drum fuel pump just by plugging it into a Wx, because the external pins are always live, you needed a battery to energise the third pin to get the SK to provide the power.
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