The voltmeter is easy to wire in. You will get your most reliable results if you connect it directly across the battery...as in one lead to battery + and one lead to battery -. it wouldnt hurt to throw in a small amperage fuse as well...something like a 5 amp or less would suffice. The voltmeter is not a load but if one of your wires wears through and grounds out you will have a fuse to blow before the wiring burns up.
My intuition nearly makes up for my lack of good judgement.
Just installed my new trolling motor