I think its time to give in and buy a new wiring harness
It seems like just about every connector is troubled. Jiggle it a little and the test light comes on, twist it a bit and the light goes out
The connectors themselves are not difficult to trouble shoot.
When you got one that is trouble, put down the test light and use your eyes.
Are the plastic connector housings together?
Are the metal terminals in the housings connecting to each other?
* if the locking tabs aren't holding, metal terminals will back out as the connector is pushed together.
* if the spring like features of the terminals have opened they won't hold tight.
Check the wire crimps to the terminals. This is a real weak point, insulation sometimes shrinks, easy location for oxidation, and if the cable is not supported properly or been yanked around the conductors can get unwound.
Check for corrosion and oxidation.
These can be easy fixes, but can also require new terminations, and sometimes even new wire if the conductor is oxidized or untwisted under the insulation.
Most of the harnesses have some ( a little) slack that will allow new terminations to be installed without spliceing in wire. But some locations, especially in the instrument harness, there isn't.
