Foot controls do get old. That is the weak link on my 37 year old Viking and I've been told there is no Viking replacement for it as they no longer support a machine that old with parts. One repair person told me I could get an aftermarket for it for $80-$100. In this particular foot control there is a resistor in it that regulates the amount of juice that goes from the electrical plug to the machine. There is a way to adjust the amount but on this particular one it has been adjusted to it's furthest amount. The foot pedal is overheating after I use it a bit. We were told by another repair person that the resistor could be bypassed with no danger. We haven't tried that yet.
Some machines have easily replaced foot controllers, others not so much so. The foot controller to my Viking uses the same cord as the one that plugs into the wall and then a special plug that goes into the machine. My newer Janome has separate cords for the power and the foot controller and the end of the foot controller is like a jack.
You need to be careful when getting a new foot controller, even if you splice and wire it in to an existing cord, that is it compatible with your machine. It not a one size fits all kind of thing. It's tempting when you do an on-line search on foot controls to be lured by the $20+ ones when you've been quoted $100+ at the repair shop to get a new one for your particular machine but be careful doing that.