Take a test light, and attach it to a good ground......now probe terminal 16....light should be bright.....now attach the test light between 4 and 16....if the light is bright like before, the ground at 4 is ok...
Not sure if you can take it apart to clean the corrosion......otherwise, you can string like three or four of them together, and solder them together with an external wire with an eyelet on the end, drill a hole in a convenient place, preferably above the water , and screw it into the body somewhere, creating your own ground....
DLC....data link connector
