Hmm - I'll beg to differ on the upgrade; - unless you mean you are significantly increasing the value of your Nova by adding a few feet of copper wire and a relay

The blue/yellow is an engine running signal so the relay won't switch on and drain the battery without the engine running. The light bit was a typo...

BTW don't be tempted to connect that right wire straight to the battery without the 60A fuse. Unless you like loom fires that is...