It's pretty similar to what I already have. I've just realised how dumb I was being, the symbol for the cigarette lighter fuse is a burning cigarette, I didn't make the connection (no pun!) for some reason, derrp. Thanks! I'll try that.
Last (dumb) question, is there a bolt close to the fuse box I can earth to? I've prodded around with a multimeter and can't find any with continuity.