I'm pretty sure with electric brakes it doesn't matter which wire and your just creating a circuit but maybe confirm that with someone that's certain!
I did have issues with mine on my last van and was told its important to run decent cable from plug to brakes (I was told 6mm cable) and I was also told to run a feed from plug to each wheel or set of wheels separately not loop from one to the next. I did that and had no further issues.