Not trying to be difficult, but problem not solved is not specific. Sounds like you have done cleaning and visual of connectors, but what does the meter say? If you have voltage at red/black ammeter connections, the next step is going further from there on schematic. Looking for voltage at switch, fuse box... If no voltage at red/black then what you think is good is not, or the following about ground could be the problem.
There is an engine to body firewall ground at rear passenger side, above heater fan. If it is broke, measuring voltage from engine ground will be good, but not from body. So, without it, body electrical will not work unless grounding by linkages and bearings, a very bad thing.