Wiring help for trunk mount battery

^^^^Yep. And when I say "Ford starter relay" I mean the ones used on Fords. There are lots of different types of solenoid relays, and they all look vaguely similar. There are several different ways they are wired, along with starter vs continuous. One great example of an oddball is the AMC "Ford" one which has an extra terminal for the NSS along with the usual "Ford" terminals. It is NOT a 'grounded base'