My tach is all wired up. Now I just need to get the motor built and in there. Should I install a fuse in the igniton fed wire of the tach just to make sure it stays safe? If so what amp fuse?

Installed an Autometer 5 incher a month or so ago on my 67. I wired a 4amp fuse into the circuit as advised by them into the "hot" wire not the one from the "tach" wire on my HEI. Cheap protection, less than 5 bucks and 10 minutes time.

I have the hot wire plugged into the ign. part of the fuse box. Will a 4 amp fuse be big enough?

4 amps is my esimate also. Greg is close to what I see. The fuse is only trying to protect the gage. This should be an in-line fuse to the gage. Leave the larger one in the fuse panel. GM did not do a good job in this area. Normally the over fused everything by adding other things on the circuit.