Maybe I've missed something, but it seems to me to be a lot of work for not much improvement. Disabling one locomotive's motor to add "power" to another locomotive doesn't make much of an improvement in the pulling power.
It would have been easier to simply couple the two locomotives together in order to pull a heavier train, and if the train was longer and heavier, you simply add more locomotives....no need for adding more wiring and no need for soldering anything, either.
Wayne
This was a fun project that gave new life to a great looking (but still outdated) Athearn Blue Box locomotive.
https://youtube.com/watch?v=rIQsDqHBTu4&feature=shares
Harrison
Homeschooler living In upstate NY a.k.a Northern NY.
Modeling the D&H in 1978.
Route of the famous "Montreal Limited"
My YouTube