12v Loss To Can Line

I can only suggest, go back to basics. Get the wiring diagram, choose a mid point in the relevant circuit and check for voltage. If as expected, halve the second part, same again, repeat until no voltage or low voltage. Then work back until good voltage, finding the fault.
Similar backwards, if no or low voltage at initial mid point. Connectors would have to be initial suspects, particularly earthing points. If those are dirty, well worth taking off & giving a good clean, then refit & grease up, to protect.

Hope that helps. Good luck sorting the problem.