Now there's your problem
I have been trying to track down some issues on a 90 VN750 that I recently purchased. Yesterday I was riding slow and the temp gauge was nearing the redline. Running at highway speeds brought the temp down, so I suspected the radiator fan. When I grounded the temp switch connector the fan would not turn on. More tracing of wires until I finally decided to bite the bullet and remove the junction box and peek inside.
The corrosion looks to be a combination of battery acid and heat generated by increased resistance.
If you are scratching your head at electrical problems, drilling out the plastic on the back side of the Junction Box is not that difficult (just use a 3/16 bit and drill down ~1/8") Then go around the edge with a flat screwdriver and pry the case apart. It seems pretty easy to put back together if your circuit board is still good.
I got a new box on order, but came away with 2 good lessons. MF batteries are good and don't be afraid to open stuff up.