@
humfrz
From your post I'm assuming then that your 1970 MGB had 2-6V batteries behind the front seat like my 1964 did. My MGB had a positive ground system. I replaced the batteries and hooked them up to negative ground, fried a bunch of wires.
Just Googled it. From 1968 on they switched to negative ground.
http://www.mgexp.com/phorum/read.php?1,1608742