I've just bought a plug that fits my K75 power socket and I was wondering if I could connect the plug to my battery charger and plug it into the bike socket instead of clipping the crocodile clips onto the battery terminals.
There were no wiring instructions with the plug but I'm assuming that the central pin is the live connection.
Can anyone advise?

That's what I've been doing for years, just upgraded to a 750ma 'Genius' charger that has multi-mode charging & can be left plugged in all winter (which is farkling long here)  

On the plug I got (from BMW) the leads were red/black - kinda obvious... if yours isn't colour coded just plug it in & put a meter on it...  

Lorne

The center terminal is the plus terminal.

Yes, the centre tip is positive. Most chargers nowadays are polarity protected. That means any dummy can pop the wrong clips onto the terminal posts and they won't get a light and spark show - because there has to be enough 'juice' left in the battery for the charger to 'recognise' the battery is whatever fraction of 12 volts is required to induce a charge. But it also means that if a battery is low enough to not accept a charge, none will be forthcoming.

I also use a Genuis brand charger (the G1100 baby one) and it works a treat. Battery Tender brand, which have been the cause of many an overcharged (dried out done for dead) battery at Winter's end, are now equipped with a 72 or 80 hour automatic shut off circuit. It took yonks, but they've acknowledged the problem.