I'm burning in my new tonearm cable right now, I just made up a custom wire rig to do the job better and faster.
Bought a cheap Radio Shack RCA/RCA and cut off one end. Stripped the conductors to reveal hot and ground. Soldered hots and grounds to a male 5 pin DIN and plugged it into the female DIN (to RCA) of my new phono cable.
Hook Shack RCA to source such as FM tuner or CD player and the RCA's on your new tonearm cable to a high level input on your preamp. Turn on your tuner or CD player on repeat and let it burn.
To be sure you're OK, you can listen "through" the tonearm cable and shack wire to verify signal is passing through both channels.
If you need to break in head shell to preamp, solder alligator clips on the stripped Shack cable (instead of male DIN), plug Shack RCA's into tuner or CD as above and clip alligators on head shell leads (Keep away from cartridge!).
First description burns new cable only. Second method burns head shell leads, internal wire in tonearm and tone arm cable to preamp.
Good news, cuts hundreds of hours off of spinning LP's to get wires broken in and the FM or CD source is over one volt, many times the output of phono cartridges. Many moving coils are as low as .1 to .5 MV, meaning they never push enough voltage through your new wire to settle it.