I"m not lost and want to express my sincere gratitude to all who responded and especially Hotrod and Bartamos. Albert Einstein is widely credited with saying, “The definition of insanity is doing the same thing over and over again, but expecting different results.” That is where I was at a few days ago, so after talking it over with a couple of knowledgeable friends, they were convinced it was a grounding problem. So I removed all the ground wires in the lighting circuit, including the ground strap to the truck frame, cleaned the surfaces, scrubbed the connectors with emery paper, rechecked the wiring diagrams and harness connection instructions by the harness mfger. All were correct and the circuits checked out until I plugged the headlights into their sockets. The split voltages re-appeared and the red light stayed on. So I bought a new pigtail, hooked it to my spare dimmer switch and with the headlight hooked up got the same results. I don't expect I will be driving the truck much at night so reluctantly decided to lift the lo beam wire so only one element works and signed on today to let you all know. Then I read your last response Bartamos and then understood what Hotrod was saying. I knew immediately that the wiring from the headlight pigtail was not terminated correctly. So, now the headlights work as designed and I can move on with the remaining punchlist items to complete the truck, but expect that it is never going to be "complete". It has been a memorable project though and this is just one more for the memory book. Thanks again for your help.
I mentioned in my first post that the circuits were terminated as diagramed in the GMC Trucks Maintenance Manual schematic, with the Hi and Lo wiring terminated on the sides of the socket picture and ground between the two connections in the middle of the picture. There is no mention in the Lighting System section of the correct wiring for the headlight socket and it wasn't specified in the harness manufacturer instructions either. So a heads up for anyone who may take things literally as I did.
