Need Help 240Z tach

I am new to the forum. I have a 73 240 (w/ 72 carbs). I am restoring it and have a couple problems. I'm hoping there is someone who can help. The tach was completely out of dash and recently re-installed. It had been reading about 3000 rpms when engine was idling at about 1000 and needle was bouncing. I figured it was a bad ground. After securing it into brackets, I cleaned the terminals at coil (I know one of the wires goes to tach). When engine started, tach worked perfectly for about 15 minutes, then it went to zero where it remains. Any ideas? Second problem is that I am getting a drain from battery of about 2 amps. If I remove fuse that radio is on, the drain stops, so it must be that circuit. Is anything else on that fuse besides radio. Thanks for any help.

probably cooked the fuse for the gauges, the drain could be caused by a partial short... if you can find an fsm online it'll probably give you a wiring diagram, and if you do let me know cause i'd love to have it...

but if it's like the later model z's i'm pretty sure the radio is on its own