That's always good advice, but I'm not going at this blindly. Probably I should have specified all this at the beginning, sorry about that.
I got code P0130 for bad heater in the forward engine side O2 sensor, (which I didn't get before I let some hack work on my truck.) That's on page DI-43 in the FSM, which also refers to a page IN-28 that I do not have. The EWD shows on the Engine Controls page 58 that the heater wire should be gray at the harness side coupling, with the ground being yellow and red. Since I may have a problem on either the pos or neg side of the heater circuit on the bank 1 sensor connector- which is original to the truck and definitely showing it's age- I'm electing to get a pigtail to replace the entire coupling, and I found a unit from Ballenger, #CONN-85928, that should work. Hopefully this solves my problem. If not then I need to go further back up the harness chasing those wires. My other option would be to unpin the connector and try just replacing the two affected wires and terminals, but I've not had great luck unpinning connectors on this truck without breaking some plastic. I'd rather just replace the whole thing and have a new coupling.
I'm pretty averse to poking holes in wire insulation for testing because I'm high in the rust belt and the road salt just wreaks havoc on unprotected wiring. I've had wiring fall apart from corrosion under the insulation at old test probe holes, so now I really try not to compromise wiring integrity unless I absolutely have to. Hopefully I can remember to put all the adhesive heat-shrink tubing on BEFORE I start crimping things this time!
Thank you for all the part numbers of all the components, that helps a ton on these old rigs!