There's no quick fix, I'm afraid. I think you're going to have to be methodical and work your way through each problem - chances are that fixing one thing will fix other things. Disconnecting as much as possible then connecting one thing at a time, checking it works, then moving on, is how I approach things like this. If you've got 20 different issues and you're trying to solve them all at once, you'll be there forever.
It looks like someone has done some bodging in the past (I've no idea what that big fat cable is for in your Landy - I've got one like it in mine that I put in to feed the power amp!) So be prepared to do some repair work. Get some connectors, a decent set of crimpers, a multimeter, a soldering iron and some heatshrink.