A casualty of the wiring locker re-wire was the GPS connection for the Raymarine Autohelm system. The previous install was temporary, and used two chocolate blocks to bridge the three wires for the ground.
The existing cable to the GPS uses red (+12V), yellow (data), and black (power ground and signal ground). The Raymarine gear has a red (data) and blue (signal ground) cable. My power supply cable is red (+12V) and black (power ground). In other words, a pain in the rear to keep straight. The chocolate block solution was a bit precarious, and easy to knock/catch/damage.
To validate which connection went where, since I failed to take a photo before discombobulating everything, I used some Wago connectors. These are bridged bits of metal and plastic with spring-loaded clamping action. These made it easy to test the data/signal/power connections before soldering and heat-shrinking. They’re designed to support 240V power cables, and are probably overkill on a boat, but are so much easier to work with compared to chocolate block terminals.
The +12V is hooked off of the chart table switch labeled “Autopilot”, and the ground is terminated with a fork connector that’s doubled up on a negative bus terminal on the fused bus. Alas, the doubling up stops the plastic cover from going on, so I probably need to move some stuff around. Tomorrow perhaps.
As an aside, soldering three wires together, and applying extra solder, with just two hands is kinda tricky.
Putting the Wago connectors on the GPS-bound cable 
Everything bridged together in what I hoped was the correct permutation 
Soldered and heat-shrunk 
It verks!