C-Fused is right about 28 gauge silicone coated wire being the best you could use and is perfect for all trains where the wires run through a coupling and have to move a lot.
As another option is something else that works great and it has the black and red wire together so its easy to fit around small spaces. I have about 5 spools of this on hand so I never run out. One spool is probably enough for a lifetime but I never want to run out and find that it is discontinued.
Model Power 2 Conductor Wire
You might also want to just jump those wires you can see to make sure it will work and nothing else is wrong before disassembling the the engine and tender to install the new wires.
As another option is something else that works great and it has the black and red wire together so its easy to fit around small spaces. I have about 5 spools of this on hand so I never run out. One spool is probably enough for a lifetime but I never want to run out and find that it is discontinued.
Model Power 2 Conductor Wire
You might also want to just jump those wires you can see to make sure it will work and nothing else is wrong before disassembling the the engine and tender to install the new wires.