UK Car Repair: 1986 XJ6 Electrical Problems, chevy conversion, light fuse

Question
   Aloha and Happy New Year from Honolulu! Have a 350 Chevy conversion with major battery drain problems! Went through 3 new Napa batteries; then starting was fine with new Gold Die Hard; and now it is dead after positive cable was disconnected for 2 weeks!
   Voltage Guage showed 13 volts when last running and multi meter showed battery holding full charge! Think have narrowed it down to 8 male prong Ballast relay on center firewall! What do you think? Thank You for your time!     Grant

Answer
Aloha, Happy New Year to you too. I once had a house on Kawai. Firstly, when you disconnect the battery always take off the ground cable first, then, when reconnecting, fit the ground cable last. I know of no 8 prong ballast relay on the firewall. Just to the right of centre there is an 8 prong Fuel pump/Injection relay!  You have to establish what component is draining the battery. To do this, disconnect the ground cable, then, fit a test light between the cable and the open battery terminal. If there is a draw the test light will be lit. It is best to first remove the interior light fuse, as with a door or boot open there will be a draw.  Now remove each fuse in turn until the light goes off, this will tell you which circuit the draw is in. Most often  draws like this are because an interior/boot/glove box light is not switching off.