Lets relax, take a deep breath and smile

I understand your frustration, and you understand that this is internet, a place with 99% random unrelated shit and 1% of solutions.
Multimiter is a good rout, i am with you. So, if you don't get any good solutions on your inquiry about engine harness, grab a manual and start going through the wires. Best way to ask about this is to take a screen shot of the page from the manual, point your finger at what you don't understand and directly ask about it.
There are people here with tons of knowledge about electrical, who can look at diagram and tell you what is what, they can help you with this, you just have to properly ask. Everyone's comprehension is different. You will type one thing, and people to grasp it in 10 different ways. And then there are those, who just like to type just to type.