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Service Manuals – MyMopar
It sounds like you can use a VOM, attached is a link to a free downloadable service manual with schematic. It seems you are not getting power to your dash area. Perhaps tracing the wiring will help. All the best!
I have the '67 Plymouth manual and the Barracuda supplement. Have wired electronic circuits and done alot of house wiring. Even wired AC and DC circuits on a sailboat but auto wiring seems to be a different animal. Using a VOM is how I knew there was no power going to the circuit boards. The wiring diagram shows 5 orange wires spliced that may go to the gauge/dash light function that were not there in the old wiring and not included in the new harness. Wondering if I need to make one???