For a task like this, even the simplest non-professional cable finder can be worth its weight in cold. I must admit that I probably wouldn’t have found my red autopilot cable behind that blue cover if I hadn’t used my Schneider Electric Thorsman cable tracer device (not that the brand matters, I just happened to have one at home).
If you’re stuck, it’s worth investing £50 something like this. Quite easy to use:
1. Unplug that Mate n Lok connector and connect the red line on the transmitter to the right pin
2. For improved SNR, also connect the black ground to your normal electric ground on the boat
3. Switch on the transmitter and that pen should go ‘beep beep beep’ whenever your close to your lost cable
The signal on this non-pro devices tends to be weak and unreliable, but still helps to triangulate the location.