I installed an entirely new motor with all new accessories. The alternator however was a rebuild. I finally fired up the motor yesterday, and the fuel injection computer only shows 11.8 volts with the engine running. This leads me to either an alternator wiring issue, or bad alternator. Tell me whether the test I did should work.

I turned the key to run thus energizing the alternator exciter wire, and removed the output wire. After attaching a volt meter to the output lug I wrapped a string tightly around the pully and gave it a very fast snap spinning it at least at a rate it would achieve during idle. This produced a whopping .4 volts. Is this even a valid test? Seems to me I should receive voltage close to 14 volts with this method. Any input is appreciated.

Depends upon the type of alt installed, ie, external or internal regulated.

If ext reg, the field excitation wire would have some, a couple of volts, depending upon load, to supply the field to produce the charging voltage required. Also, a quick field check would be to place a screwdriver perpendicular to the rear bearing and feel the magnetic draw against the screwdriver.

If int reg, sensing wire should have battery voltage on it. Also, the screwdriver trick works well.

As a last resort, one can take the alt/regulator to Advance Auto for a free checkout.