I have a Livorsi GPS speedo that I purchased from Fred (Trick Marine). There's three wires Red, White & Black. I connected the White (lamp) to the green+ that was on the old speedo which only goes on when accessory toggle is flipped on, Black went to the other black off the back of the old speedo. My question is, where does the Red 12v go?

The Green & Black from the old speedo is linked together on the back side of the gauge by a twist in light that touches two metal plates. So, I'm confused where the Red GPS wire should go so it's live when ignition is turned on?

your old speedo probably didn't require an ignition signal, so you will have to pick one up from another guage. Your options include the + on the volt or tach amongst others or you may have an ignition signal available off the switch itself. Easy to check with a test light.

Youre old speedo didn't need no power to work. The two wires that were hooked to it were for the light only. If your boat wiring aint been F'ed with to much you should be able to tie into any purple wire behind the dash but use a test light and make sure it is actually ignition hot, some people do some crazy krap with wireing and I don't assume anything anymore.