I assume you do have the System SC1000 Tach & Speedo - two-gauge instrumentation
It looks like you have a cable missing- unless this is already installed on your boat!!!!
The cable that connects to the speedometer gauge is P/N 879978T
The cable that connects to the Tacho is P/N 879979T
Both of these are standard lengths of 3ft.
From your photo, it looks like you have these two and these are plugged together, which is incorrect.
You should then have a cable (wiring harness) P/N 879981T_ that comes in various lengths to suit. 10,15,20&30ft. The "_ " bit denotes the length.
Then you should have a junction box: P/N 878492T_ with 4,6 or 8 terminals - with 4 being std for single engine installations.
These two cables from the gauges go into the junction box, as does the data harness from the engine. These are all blue shrouded – not to be confused with the usual one that comes from the throttle box.
At the outboard, this wiring harness connects to the ECU at the engine via a multi plug, and also has a multi plug to connect to the pitot speed sensor that comes up inside the leg/mid-section (I think). There are also 3 bullet connectors at this end that connect to the trim/tilt sender - BLK, YEL &?
If all this is obvious – apologies: just remembering what I worked through when I was trying to understand how it all related and linked after tidying up the “professional” installation of spaghetti