Its not rocket science, especially if you have Lionel 180W bricks with the factory connector still on. That connector plugs into the Legacy Powermaster. Then on the LPM are two studs, 'A' and 'U'. 'A' goes to the center rail and 'U' goes to the outer rail. Then I daisy chain all the 'U' terminals together to the Command Base, but I'm not sure if that is necessary. Having correctly sized ring terminals (for the wire gauge, and for the threads) sure helps. There is no wiring up the serial data line, the LPM have a receiver for the 455 kHz track TMCC signal that the Command Base broadcasts.
There is another way. I have three IC Controls version of the TPC, I could send them to you for free if you agree to give say $60 to your favorite charity. One of them has an early version of firmware that didn't work well with PS1 electronics (supposedly) and for sure did not work well with Electric RR mini-commanders, when in CONV mode. They have been sitting in my basement doing nothing ever since I got the LPMs.