Jean,
I doubt if electrical tape would help much. Again, a trip to an electrical supply house might be fruitful.
Keep the connector block, but if you want you can toss the cord, it's toast ..... LOL.
I sew slow most of them and like a controller that will start slow and smoothly increase the speed. Jerky ones irritate the dickens out of me.
Here is a blog by our own ArchaicArcane, she's got a complete section in there about overhauling controllers.
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http://www.archaicarcane.com/about/ }
If you look on the right you'll see a couple pics of foot controllers being worked on. Click on 'em. I do pretty good rewiring them, but she's got tips on tuning them like you need.
Joe