S10xGN
The green wire does ground the body of the solenoid. The black and red wires operate the coil inside the solenoid. The problem is that the controller turns the ground on and off (pulse width modulation) in order to control anything less than 100% on "injection control". By tying the green and black wires together in the connector, if any part of the kit is grounded (line, tank, solenoid) and can pass that ground to the body of the solenoid, the solenoid will open and not cycle untill boost drops below the turnon point.
If you want to test it without being dangerous, turn off the tank, give it enough boost to activate for a second to purge solenoid and regulator, then you can use a mighty vac or other pressure source to activate it without injecting propane. With the "injection control" set in the middle (slight detent you can feel) and enough pressure to turn it on, you should be able to hear the solenoid constantly clicking on and off about 3 times per second. If you don't, it is because the grounds are tied together. Now cut the green wire at the connector and it should click on and off as originally designed.
If you are running it at 100% (fully clockwise) on the "injection control" then doing this won't make any difference since the solenoid will see a constant ground from the controller as well as from the green wire. It doesn't effect the solenoid turning on, just it's cycling.
HTH, PM me if you are still confused.