Re: 1972 25 hp Evinrude push button start.
Ive never worked on one of these.
Im sure it can be done.
First you need to look at the solenoid and find the wire that goes to the small +ve terminal. (the neg will be the small terminal that is gound out on to the motor right by the solenoid.
That small +ve wire will need to be hooked up front to one side of your stater switch.
The other side of your starter switch will need 12v to it from the battery.
Now if you have a electric choke then you will need a switch for that too, you can use the 12v line from the battery that you have run up front to power the starter switch for that so that you dont need to run two battery 12v lines up front.
The next part is easy but im not sure how it works on your engine. On some engines of that age you need to keep the magneto powered to run the engine and you ground it to stop it. I dont know how that works so someone should hopefully come along and give you the advice on that part but this above should be enough to get you stated.
Try running marine wire if possible, its a little bit more expensive but it has different elements tinned into it so doesnt corrode anywhere near as quick as normal wire.
Put in a fuse too
