Does anyone know what Raymarine electronics are looking for on the sense pin?
Yes. A very small resistance (cable resistance) to ground... but that doesn't seem to be relevant to the rest of your post.
Having done something similar recently, I'll try to help, so, stepping back a bit:
It seems the Raymarine "RP58" you refer to might be a "P58" instead, details of which are found here
. The Airmar site lists the following wiring diagram for the P58:
The white, red and green wires you are referring to are shown as white, yellow and orange on the P58.. Confused yet? I am.. but let's move on:
: Basically, Raymarine's newer displays use "2-wire" transducers ("Voltage/Signal" + "Sense" lines) whereas the older ST50 displays and transducers are "3-wire" ("Voltage" + "Speed" + "Ground"). AFAIK
, you can't directly interconnect the two types and expect it to work any more than you could directly connect a US made 110V appliance into an Australian 240V power point...
: Assuming you've connected up the Blue and Black wires to their mates on the ST50 transducer, the only other thing the E7 might need is pins 6 & 7 "Ground" connected together - the 'green' wire is not used for depth... But all that is assuming the ST50 transducer you have is a 50/200kHz transducer - if not, it won't work whatever way you hook it up.
Summary: IMHO, it's be easier to get the P58 to work with your E7 display than your existing ST50 transducers.
I hope this helps.