Thanks all, good news that it’s easy. Tim, could you let me know where you got your bits pieces from, please.
Yep, that's the place to go. I've used them for years, excellent service. I used a couple of lengths of 3mm 27A cable (red and black), a couple of ring terminals, an inline 20A Blade fuse, brass bullet connectors and sleeves, spiraband wrapping, and an external accessory socket.
I drilled a hole through the rear bulkhead just above the transmission tunnel to pass the wires through, and connected the accessory socket to the wires with bullet connectors. The wires were wrapped in spiraband and ziptied to the tubular crossmember. The ring terminals go on to the clamp bolts for the battery connections, and were soldered to the wires with a bit of heat shrink to keep everything neat and tidy.