I am having similar issue and have done a lot of research on this but my engine is 75 HP 1996 model. What I have learned is how to check the rectifier to see if it is still good or not. The burnt wires could be from a loose connection an the point of the burn. The current going thru those wires if you have a bad connection will cause the wires to heat up at that connection and cause them to burn.
The rectifier test should be performed using a Volt ohm meter preferably Electronic VOM with a diode/rectifier test. Depending on if the rectifier is a germanium or silicone rectifier the voltage drop reading should be either close to .3 or .7. Anywhere around .25 to .8 is a good reading for a rectifier since you will no know if it is a germanium or silicon. This indicates that rectifier has a good voltage drop.
Use the Diode test if you have one other wise using 2k ohm the test will only tell you if rectifier is shorted or open and not if it is actually dropping voltage one way and blocking voltage the other way.
The above diagram using the red meter lead to ground and black lead to a yellow lead. the reading for Diode setting should be around .5 do this for the other yellow lead too.
Then using the black lead on ground do same check on yellow using red lead the reading should be infinity or open.
Then check first black meter to a yellow red meter lead to a red it should read open or infinity. Do this for the other yellow too.
Now reverse the the meter leads and put red meter on the yellow and black meter on the red. The reading should be around .5.
If these readings are within the above specs then the rectifier is good. But if any of them are not within specs then the rectifier is bad.
