I’ve put the debacle of the micro connectors and missed resistor behind me, and as I said, I’ve decided to revert to connectors I know and trust. These are harvested from an IC socket, and are quite robust, but also big. Okay, big is relative in our world: I often tell people that a lot of the parts I deal with they would happily sweep up as dust. Our parts wouldn’t even rattle in alarm as the vacuum cleaner sucked them into its void.
However, while small at normal people standards, the IC connectors are about 5 mm long and 1.5 mm in diameter. Putting that into perspective, they are about 18″ x 6″ in HO scale; imagine hiding several of those on this little teakettle! So, I have resigned myself to perverse permanent wires hanging off the back of several subassemblies. At least they will be proper wires, not those pesky hair-like magnet wires.
There was a brief panic when the headlight wouldn’t come on. I only realized it was because the engine was in reverse after taking apart and testing much of the harness. Reversing headlights are a useless feature on engines oil lamps. Can you imagine getting out of the cab, making your way to the front of the locomotive, climbing up on the tiny step on the side of the smokebox, opening the lamp to extinguish the flame so the engine could reverse? In a blizzard? No, these headlights went on at night on the main track, and stayed on until no longer needed.
Pembroke:87 
After all that work, at the risk of being physically assaulted, in the O-Gauge world the locomotive tender connection is made by wireless connections in Lionel Locomotives. I think MTH has gone that way too. I don’t pretend to know how this is done. Both are now making HO equipment, but I don’t know if their locomotives have the same technology.
Clearly O Scale magic!