Not specific to Bluewater or any brand. The upper station cables will lead to the lower station control. The control itself has push-pull connections to handle
remote stations.
The lower station will have the cables that run to the engines.
Quick check would be to pull out the upper station control and disconnect the cables. If the lower station works then you know it's the cables between the lower station to upper that are the problem.
Be sure to take a picture of the cable connections - washers, cotter pins, spacers, whatever - before you disconnect them. Also measure the adjusted length of cable ends & control stop points for reassembly. There are many adjustments on both ends of the cables, also travel stops on both throws of the controls. Not rocket science but VERY time consuming to get all adjustments dialed in.
Once you find the problem cables, look at the ends for markings that tell you the length so that you get the correct
replacements.
Good luck.