A couple of brake system questions.

I have a 1981 Maxim 650.

After seeing all the posts on here about general maintenance, I've decided to replace the back brakes, install new SS lines, rebuild the caliper, and install a new MC (old MC broke when PO dumped the bike).

Question 1: Will I be able to use this MC with the stock wiring?

Question 2: Should I replace the caliper piston? I don't know if the corrosion is a concern.

 

Wires are wires, so if you are handy with a soldering iron and a wiring diagram you can pretty much connet anything to anything else (with the exception of "smart" parts like ECUs and such).
As a general rule I don't like to leave any corrosion on things, no matter if they present a genuine concern. That being said, that surface of the piston is exposed to the elements as the back of the brake pads do not form a complete seal with them, so they will generally look like that all the time. It wouldn't necessarily hurt anything, but like I said I'd go ahead and remove it on principle. Once you clean it, do not use oil to protect the metal as this could run out onto your pads, use a light polish like Nevr-Dull to protect it.

 

Thank you! I think I have some of that polish about the house.

 

I would clean up as much of the corrosion as I could, but I wouldn't worry too much about trying to get the inside of the piston to shine like chrome either.

Where you'll run in to problems is on the outside of the piston. If the old caliper seal let any kind of moisture inside the caliper, that's the corrosion you have to be concerned with.