What is this wire for?

[fishone]

Yesterday I was watching dock attendant put my boat away on to the lift. Engine stalled and when he tried to start it and the starter would not turn over, and then it did? sounded like a dying battery? I checked it out and see that one wire on my starboard side battery is corroded. its not the pos. and not the neg. ( black wire on neg. side and its kind of a soft wire ). I believe its corroded where its crimped to the lug. it has a heat shrink wrap over it so you cant see it but when I wiggle it, feels like its very flimsy? I know it goes to the engine but I didn't have time to trace it . doe s anyone know what this wire is for?

 

[fishone]

I believe it is the engine ground. I'll cut back and put a new lug on the wire and see if it corrects the problem.

 

[BigI]

I have the same problem but my symptom was sluggish starting. My engine power cable was corroded at the lug to wire connection to the point that only a pencil lead thickness of wire was left. I pealed back the insulation and the wire was black and tarnished on both + & -. So, I'm replacing the whole power harness. I'm making one up myself. In retrospect I should have just bought the harness pre-made.