Ive got a 73 240Z that wont start, everything electrically poweres up when you stick it in the accessory position, and likewise when in the "on position", but when you try to crank it over, the battery voltage drops to next to nothing (and drains quite a bit of power).
I replaced the starter, wasnt that, i checked the ignition switch, i *think* its ok from what i tested. any ideas?
I'm with Sky on the battery thing, also, check the connections on the starter and leads from the battery to the back of the starter. If they are loose, they can't carry the heavy demand of the starter. But enough contact will allow the use of acessories but you won't reconize the problem right away.