PS3 Diesel - 3 Rail / 2 Rail switch, 20-20271-1

You can rewire and eliminate the switch if you never intend to run 2-rail, it's actually a somewhat troublesome component on these anyway.  It's a cheap switch and it carries the full current for the locomotive.

Any generic switch with the same poles would work. Like John says they are cheap and made poorly. Inn most cases they'll hold up and do the job.

I've found one burned out and another dead from the factory. The PS2 polarity switch is the same quality and I've found those DOA as well. That's important for running in 2 rail mode on older models.

 I've even found a smoke pot that shorted out when turned to zero. I believe that was from rough handling?

It's good to check out all avenues when troubleshooting. The techs have a board tester to narrow down what's wrong. I've used known good working frames.  .....

Before I get corrected please don't put a good board into a frame that maybe shorted!

  That's not correct troubleshooting. That's asking for more trouble.

Wire nut the correct wires together.  Eliminate the switch.

What was the dead short?  Chances are that short was left on for a while an took the switch out.  So you can do either, eliminate or get another.  G