I installed a new 240z motor and new alternator. When I connect the F N wires to the alternator and turn the key to the on position the amp meter goes to -45 amps and the ignition fuse blows. What can I test to see if the new alternator is bad.

I fixed the problem. The F and N wires in the alternator were wired incorrectly. After fixing the wiring in the alternator no more blown fuse and the alternator works great. They had shorted the F and N wires in the alternator when the alternator was assembled.

Ouch. I hope it didn't cause any other problems in your electrical system.

By F&N wires, are you referring to the "T" shaped plug that inserts into the back of the altnernator? They reversed those when they rebuilt it??? What a jip. I'd return the damn thing & ask for them to pay for my blown fuse & whatever else it affected. Hats off to you sir for figuring it out.

Typical quality control... we were just complaining about a leaking header... if the simple pressure test was done, or in your case a spin on a jig then these problems would never leave the factory...

My observation of many of today's car parts suppliers......they are starting to polish turds pretty good.