Battery Maintenance Charger AMV8

Hi all I am new to the forum and AM ownership but have had the usual gamut of exotics along the way.

My question, put simply is, is there a fuse for the circuit which the battery maintenance charger uses, if so where is it located please.

Greater explanation, I have reasonable automotive experience for a non prof AND I have RTFM. I put a multi meter on the plug in the boot compartment to check the polarity and made up a lead ( by the way the third inlet is defunct there are only two wires connected to the top and bottom sockets) to connect to my trickle charger. It has worked fine for two weeks but today when I plugged it in the charger showed power but no condition info back from the battery. The same multi meter test showed no voltage reading. I took the socket out and traced the wires back to a jack plug behind the boot fuse box which I removed checked continuity and supply to the plug, nothing, the wires then integrate into the loom. I have checked all the possible fuses that may possibly control this circuit but they are fine. Don't really want to resort to using the 12v cigarette socket as I have had the other working.

Thanks in advance Graham