Look at the wires going to the trunk relay.
This.
The instructions want you to use a relay, anyway. The trunk popper relay is already under the dash, between the column and the radio pod.
I'm not sure whether the relay has a continuous ground, and 12V is switched to activate it, or whether it has continuous 12V, and ground is switched.
(I'm sure that others are familiar. I've never had to investigate, so I don't know.)
If 12V is switched, just connect the red-blk wire to that terminal. Or to the other end of that same wire, at the dash switch.
The solenoid itself uses switched 12 volts, and is grounded through the trunk latch hook.