I picked up a used Railking steamer. I had to repair some damaged wiring and noticed that P5V is provided via the 7 pin connector for the tach led and then P5V is also made via the 2 diodes in the engine tether connector board. This seems redundant. Is there a difference in these 2 5v sources? Could the tach be run from the 5v made by the loco side diodes to free up a pin for like a front coupler?
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NO! The voltage to the tach is NOT the same as the voltage generated by the two diodes!
P5V is the 5V common that is supplied to the tach and fan motor. PV is the unregulated DC bulk power that is used for motor drive, lighting, and any coupler if present in the locomotive. PV is usually 20-22 volts DC unregulated.
There aren’t enough pins in the harness to transmit all the data/power that is needed in some steam locos, so PV is generated by the motor leads through diodes in the 10 pin socket or harness.
I've never done this but is it possible to reuse the outside rail ground wire for another function in the locomotive and pickup the outside rail power through the tender wheels? What drawback could occur in this method?
Yes and you can also gain center rail with pickups on the tender. MTH did this with some engines to gain the front coupler. Metal drawbar and pin can assist with ground too. G
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