What gauge is the main power center rail pickup wire

I typically use the supeflex high strand count 22 gauge wire available from multiple suppliers.

Just look for "Lionel super flex wire" with many of the forum sponsors.

Might be a worthwhile endeavor to try to figure out why the wire melted.

I'm also a bit confused, where are the wires to the front electrocoupler, or, did Lionel only put one wire with the other side grounded to frame.

I found the engine on Lionel's website (http://www.lionel.com/products...-diesel-178-6-28503/), but on that page, the link to the product support pdf is dead, nice job Lionel.

But I did find this:

https://www.lionelsupport.com/...7-Diesel-178-6-28503

Typically, the internal track power wiring is #22 wire.  This is actually not an uncommon failure, it comes from the engine derailing and one roller sitting on an outside rail and the other on the center rail.  If you have an old PW transformer that doesn't have a very fast or properly rated circuit breaker, things just sit there and cook until something melts.  This is why we are constantly beating the drum for good circuit protection for your layout.

I suspect it was derailed and baked by a previous accident. I have only run it a couple loops. It still runs without any hesitation.  I would not have known if I had not opened up the shell to replace the strobe beacon lens. Good circuit protection is a must.

Both electrocoupler black wires are there. This red power wire melted onto them. They appear ok. It is hard to make out in the pic.

Thank you for the replies. I will get the correct wire ordered.