I suspect you are correct, and 8 years old is a long time, so it also could be corroded, and all of them might be loose. Take a big piece of cardboard and put under the work area, this is to catch those pesky little screws you will drop. To check those connections at the plug, you will have to take it apart. Find and remove the screws (two I think) holding the inside part from pushing out, by holding all the wires at the back (where they go into the plug), push them toward the front of the plug, and it will/should come out of the housing. Now you can easily see which and what the problems are. I would use a 12v test light before I put it back together to make sure all is working first. This should fix it. Once you figure it out, and fix it, then put Vaseline petroleum jelly on all the exposed connectors and then put it back in. This will help keep it waterproof and it won't corrode again. If it has shorted out, you might have to cut out the bad part, and splice in enough extra wire to make the lengths correct before you put it back together. If this is the case, I would use a little piece of Scotch 23 Rubber tape, and then a little piece of Scotch 88 electrical tape to make that splice waterproof. Then after you have it fixed, tape over the whole wire bundle for about a foot or so, it helps keep additional water out of the thing. This is a time consuming fix, but not rocket science, unless you are not versed in electrical things, then get a friend who is, they can help you.
Monty & Janet - 2007 Alpine APEX 40 MDTS
S/N - 75715 - Retired - Master Certified RV Tech