Bad stator or bad voltage rectifier?

How would I know if I have a bad rectifier or stator?

I know about the battery test and revving the engine to 5000-7000 Rpm's and watching for a voltage drop with the headlights on but my headlight blew the last time I tried that. My fuses all test good.

Could it be the stator?

I have a 1986 FZ 600.

On that single bit of information it almost sounds like the regulator rectifier is bad and the regulator part of it is wide open. This might be why you rev'd it and the light's blew but I'm only guessing. Get a DVM and a service manual.

Your stator probably has 3 winding. Unplug it and measure the resistance on the 3 windings. Put the meter in the lowest ohms range. The resistance should be pretty equal between any two wires of the 3 wires. Then test resistance between each of the three wires to engine or chassis ground. There should be no continuity to engine or chassis ground.

You really need to get the repair/service manual for your bike. Yamahas are close in engineering but the specs are going to vary so you really need reference data and where stuff is. I know you also had light problems I addressed in another thread. If you should get a PDF of the manual, PM me. I will help as best I can.
Have you read my reply on your other thread?