Out of curiosity, pull the radio out to make sure the loom hasn't been buggered about with. The extra positive wire may be connected to the bodged loom
I say fair play to you mate. Getting stuck in and learning your way around is the way to go! I have always been into cars, and the mechanics behind them, but every vehicle has its differences, even though we are a 99% Ford family owning no less than 10 various models, the differences and similarities can be very close, but very wide! The ABS system MAY have other issues, but the way forward in my opinion is to check out your sensors first, as it is fairly straightforward. The loom may have a break in another part, the fuse is worth checking, or it could be as simple as knackered connections to the sensors themselves
If you know a good garage, or have forscan, it would be worth getting the codes read and translated.
All the best bud, and keep at it!!