oops, looks like a 5v signal? use a 10k resistor if it is 5v I guess. Sorry, not the aldl expert
according to the connector pics, it looks like 160 baud is australian?
GM 8192/160 Baud ALDL Interface and the 12 pin is US @ 8192 baud? 5 volts?
also: "Early ECUs produced a fixed 8192 ALDL data stream when the user placed a 10k ohm resistor between ALDL connector pins A and B. Later ECUs added internal receive circuitry"
so still some unknowns about baud and voltage levels and the directionality of the exchange in my head.