Well, they will send you whatever you ask them to, and it would help you if you caught an error. That would require you to know what you were looking at. For that you’d probably have to be an electrical engineer.

So you’d have to spend electrical engineering salary on checking over every little wire. That adds to cost and timeline.

Part of what you use the OEM for is so that they have to spec it out, not your expensive engineers, and get something lower cost and faster.

And frankly, a lot of things you just don’t expect that you have to tell them. Like the wire length issue in this particular post, you would expect them to just get that at least approximately correct.

You don’t know what you don’t know and it’s easy to evaluate in hindsight, but what you’re not seeing in this post is all the things they just did correctly with no prompting. There were surely very many, and each of them saved a good amount of time and money.