I bought a Echomap Ultra 106sv with a GT54UHD-TM at the transom. I want to have have an inside the hull transducer for high speed. (Old 1994 Ranger 482VS).
(1st mistake)
I bought Y cable 010-12445-33 and a GT18HW-IH based on a YouTube video and is already epoxied on to the hull.
(2nd mistake)
Did not look at what the Y cable shows will work with it. Based on the Y cable I need a GT-15 inside the hull and only a GT-30 at the transom.

Each transducer works when plugged in directly into the depth finder. But neither work when plugged into the Y cable. Looking at Garmin's web site there are so darn many transducers to view through and have a feeling I need a different inside the hull transducer and transom transducer.

Been using Himminbird for 15 years and they are pretty much plug and play. With Garmin, that does not appear to be the case.

I'm 71 years old. So can someone guide me here as to what might work using the existing GT-54UHD?

I do believe You can use "ACETONE" to take care of the epoxied mistake