Re: Force marine remote to '71 Chrysler.
Welcome to iboats! First, a little background.: The US marine control box is designed so that the shift lever and cable (inside the box) will move first when you move the control handle. Then as you continue to move the handle, the throttle cable will begin to move.
So: Are you moving the control handle far enough to see this?
The cables are held in the box itself by a steel "clip" That sets into both the grooves in the cables and the plastic box itself. If this clip is missing or inserted incorrectly, either one or both cables may not function correctly.
I do not have any photos of a US Marine box so perhaps someone else will chime in with them.
When you DO finally install the control box, in order to start the engine you must disable the shift and put the engine in fast idle/warm-up. To do this, you (depending upon box design) either push in the center button and advance the control lever or pull out the whole lever about 1/4 inch and advance it. This allows a slight opening of the throttles but will limit revs to about 1500.