I'm new to Power Boating and do not currently own a boat. However, I do go fishing quite frequently on a Buddy's 28 MAKO. Recently he asked me to assist him in checking his bilge pumps to see is they were working while on a rack at the Marina. I found that one of the bilge cables had corroded off the battery terminal. I'm fairly mechanically inclined but no electrician although I can do basic things like splicing wires and heat shrinking connections etc. which I did that day.Unfortunately, when I went to reconnect the battery I inadvertently reverse connected the battery by putting the white cable with the black cable instead of with the red cable. As we were testing the bilge, as soon as the bilge kicked on smoke started coming from a length of plenum on the opposite side of the boat above the other two batteries. We were able to disconnect the incorrect polarity very quickly thereby avoiding disaster. That was quite a sobering experience let me tell you! I recommended my Buddy get a real electrician to check things out. However, being a 23 year old boat I think he's reluctant to spend much on an electrician and ask if Id help him again. I am inclined to think that the entire length of plenum should be replaced rather than splicing out the portion that burned. I'm hoping that someone on this site can give some real guidance here. How should we approach ensuring that the electrical cable in question does not have more "hot spots"? Am I correct that the entire cable should be replaced. From what I saw it runs to the cockpit and is a main circuit. Thanks in advance for any assistance you can provide.