GGG posted:By the way this is one of those area I don't think anyone really knows. But some old tech notes stated 0 invert Serial data, 7 Keeps serial data on in conventional, 3 disables serial data in conventional but keeps chuff on. ORDER DOES NOT Matter so 34 = 43. Pulled that out from the way back machine. G
Correct. The OP's loco has one of those funky modular 103 e-units for a motor driver/conventional reverse unit, AND an R2LC for TMCC. The "3" tells the R2LC to stand-down in conventional mode, and let the 103 do its thing.
TRW