Depth transducer wiring problem

[madabouttheboat]

This is the cable end of a transducer currently installed on the transom of the boat. The old head unit is long gone but it was a Navman Fishfinder. The transducer outputs speed, depth and sea temperature. There are 5 coloured wires, brown, green, red, yellow, white; 1 bare wire and one considerably thicker black wire. The depth part of the transducer works on 200mHz.



On the other hand I have a simple Navman depth display that requires a 200mHz transducer. The plug on this is an RCA type.

I am thinking that if I choose the right wires from the selection above, I should be able to put the other half of an RCA connection onto them and have a useable depth readout. One of the wires will be the negative/ground and will go to the plugs case. This will either be the bare wire or the thicker black one I am certain. I may even need to join these two together. The other wire, that needs to go to the centre pin of the RCA connector, will be the depth positive/signal wire.

The question is: What one is it? How can I work out the correct wire? Will I damage anything using the wrong wire in a trial and error mission?

I think the transducer is Airmar, but all of the wiring diagrams I can find online suggest that Airmar use a blue wire for the depth signal in a speed/depth/temperature transducer, and I don’t have a blue wire. This is a typical wiring diagram from Airmar for a Navman speed/depth/temp transducer.



Can anyone offer any assistance or advice?

Thanks

 

[earlybird]

Is the thicker black wire in fact a co-ax wire? If it is, it might well be the depth transducer cable.

 

[madabouttheboat]

Is the thicker black wire in fact a co-ax wire? If it is, it might well be the depth transducer cable.

You are right. I never spotted it, as it was cleanly cut. It just looked like a thicker wire but is infact a coax. Think you may have nailed it in one.
Thank you