Just a note on this, for electrical problems, back probing connectors and testing the ohms in the wire harness between different locations in the wire harness can tell a good story on how "healthy" the harness is. Fact of life, copper corrodes, even a perfectly maintained machine will degrade over time, just mud, moisture etc makes the process much faster. Anyway, basically getting at the fact testing wiring generally requires a multi meter and an idea where the problem might be. A wire diagram is very helpful too (toyota tis is the best source I know of -> https://www.techinfo.toyota.com/ ).

Replacing parts is "easy", atleast to some people. Wiring is quite simple, it's the scope that's the problem, don't look at it as 100 wires, but at each individual wire, kind of like a brick house is made of 100s of bricks, but they were placed one at a time. Never rally understood why so many steer away from anything to do with wiring, and some that don't steer away do "repairs" or additions so poorly that the alterations are the problem, not the oem original harness. The wires need to be sealed, no scotch locks (no sealing), electrical tape (the plastic junk tape doesn't seal, the vinal style does to an extent, "adhesive heat shrink" is one of the best ways to splice into a harness and seal it up. The other evil of bad things people do to harnesses are the poke happy people with multi meters, they poke the insulation to test a connection, but then they leave it alone. 2-3 years later the wire is so corroded that it starts loosing connection. Simple fix would be liquid electrical tape or any other way to seal the pin sized hole, or find another way to test the wire at a connector.

Photo of scotch lock -> https://ae01.alicdn.com/kf/HTB10ycfK...-Connector.jpg

Ok, I guess rant over lol.