Re: Looking for wiring diagram for black box located on port side of engine by head.
round file = chit can.
The square box on top of the motor is the regulator. Just remove it and chit can it.
The rectifier on the side may or may not be OK. Look up the FAQ on this site to test it with an ohmmeter. If you want to replace it with something reliable, look up rectifier, modify the search with my name, and dine freely.
If the alarm goes off immediately on key on, not just 4 or 5 test beeps, then the oil alert module is bad. Any other fault requires the engine to be running for an output from the module. Any oil alert from a carbureted or EFI v6 will work with a little creative clipping and splicing. You can test the tank sensor with an ohmmeter, and the rotation sensor with a voltmeter if the module still supplies 12 V to it. No matter what, it's worth it anyway because it's obviously oiling OK.
It's a known fact that the module is sometimes poorly potted, causing them to fail from moisture.
Running without the alarm system running is like running an automotive engine without the oil gauge or idiot light connected. When oiling fails your first indication is a seized engine, or parts flying at you.
hope it helps
John