I don't know if anyone has had trouble with getting the grounding "spring" to cooperate when connecting the "wireless" drawbar to the tender but I did, so I re-engineered the drawbar with one wire to replace the spring:
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Now I just roll the tender up, slide the drawbar onto the tender pin, push up firmly, and away she goes. The ring connectors are Red Dorman Conduct-Tite 22-18 ga. I used a #8 for the loco side and filed a #10 as shown for the tender side. I removed the red insulators and soldered the connectors together with a short piece of 22 AWG stranded wire. The tender side ring connector is glued with CA to a nylon spacing washer which is, in turn, glued to the drawbar. The nylon washer has to be filed flat on the edge to accommodate the connector on the drawbar. The spring on the tender pin slides over the pin and holds at the top while providing just the right amount of pressure on the ring connector to give good electrical contact without pushing the connectors apart. I imagine this "fix" will work with all MTH steamers that use this "wireless" drawbar.
Why MTH didn't just give us an 8-pin connector arrangement with the grounding connection built into the drawbar is beyond me.