The rectifier may be bad. You can disconnect the (2) yellow stator wires from the rectifier and check the resistance with a meter. If you don't have a meter, check for sales at Sears. You can get a very serviceable digital VOM for under $20 and they usually have something on sale. I picked up a decent small one for $9.95 on sale and few years ago and it's still working well. Handy for the tool box.
Check the resistance of the stator on the lowest Ohms scale on your meter. The value will be quite low. If you get an infinite reading, the stator coils are open and you'll need to replace the stator. Neither wire should have resistance to ground, when checked with your meter on the highest Ohms scale.
More likely is a bad rectifier. You can pick up a replacement here at iboats, Sierra Marine 18-5707, for under $25. Hit the "Boats Parts & Accessories" tab at the top of the page and paste in that part number.
Something you can do before tearing into the electrical system is to check voltage at the battery when the engine is running. First, you'll want to put your battery on a charger overnight to ensure it's fully charged. Then, with the motor idling in the water or on a flusher, check the battery voltage. With the meter still on the battery terminals, raise the fast idle lever and see if the voltage increases. If it stays "flat" or decreases, the charging circuit has a problem. CAUTION: with the engine in Neutral, don't raise rpm above 2,000 and don' t hold it up there for any amount of time. Just enough to see if voltage rises with speed.
Be sure to check your wiring and connections for faults, for example the "hot" wire on the rectifier could have corroded away, and it's more common to see corroded stator wires.
I've attached a rectifier test procedure. Be sure to disconnect the battery Positive cable, then all (3) wires from the rectifier, before doing the test.
HTH & G'luck.........ed
