Hi Ian and welcome.
Not being able to easily scan etc is a real pain. i've been there.
The easiest way to know where your battery cables go exactly is to follow them. We can tell you we know one goes to the top of the maxifuse relay center on the firewall and to the starter. The ground side though went to a couple different places, one to the body behind the battery and the other side was to the engine bracket or block. But I'm not 100%, should be easy to spot.
Once you've cleaned up the battery, check the Techinfo section for the ground buss cleaning. After that, you might want to consider replacing the TPS since those are the codes you got and they can jack things up. After that I'd replace the pcm.