Thanks Wizard.
I do not need an exact answer, just planning an emergency jump start system. Since the batteries are in the boot of the disco and used as a split charge system, I have installed a fuse at both ends of the cable. (A long run of high current cable fixed to the chassis rail). I am planning to bypass the fuse in the rear with a starter solenoid, but wondered if I could get by without using a second solenoid to bypass the fuse under the bonnet.
Ed