Am i correct that with a helix gen4 mega si unit, with a y cable , when you are setting still the 2d sonar is read off the trasducer on the transom and at speed its read off the puck in the hull?

That's the way it was explained to me... Dan

Me too. But i just watched doug vanderberg video that says the splitter cable take the 2d sonar wiring from the si transducer and runs to the one in the hull. I am having some crazy issues and trying to get a handle on how it works so I can fix it.

This is the issue i am having the side scan, down scan, and 2d display start and stop constantly. Nothing else is affected. That is with the console unit only powered up. Everything else was turned off besides the ethernet switch. With everything powered up and telling the front unit to use the 2d sonar from the console unit. I get a message that 2 d sonar signal was lost about every 30 seconds. Makes me think that what ever is causing the 2d sonar to lose signal is what is causing the side scan and downscan issues. The display is crystal clear exept for the stopping and starting. Leaves a little himp on lthe screen like you went over a small bridge that was submerged. not other issues with anything else.

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That is not correct when using a Y cable. The 2D signal ALWAYS comes from the 2D puck when using the the Y cable. The wires on the 2D side connect with wires on the 2D side of the splitter. There are no wires on the transducer side of the Y cable for 2D. There is a hole in the connector for the 2D transducer pin to go into to but there is no wire inside that cable for 2D. The other wires on that side connect to the DI & SI wires of the transducer. There is NO physical connection for 2D. There is no way for it to switch back and forth. The 2D signal will always come from wherever the 2D transducer is mounted.

Check your connections and check your sonar source for both unit's 2D to make sure it is selecting off of the console unit's source. Also make sure you have the latest software installed. There was a bug at one point. I'll see if I can find the reference and tag it in this post.

Check the connection of the transducer to the Y cable. They have to lock together via the two tabs in the Y cable plug and two holes in the transducer plug.
Check for a loose shoot-thru transducer.

Disconnect the shoot-thru from the Y cable and connect it directly to the display to verify the shoot-thru is functioning properly.

Disconnect the SI transducer from the Y cable and connect it directly to the display to if all are working properly.

Doing all that will determine if the Y cable is the issue, the shoot-thru is the issue, or the unit itself is the issue.

I had a gen 2 and went to gen 3 and my shoot through sonar is no longer compatible. I had to find and disconnect the Y cable to get it working.

Its either/or.

I get much better sonar readings with my side scan, but can't get depth readings while running.

So I installed a transducer switch on my console. I use my thru-hull puck when running and when idling or fishing, I switch to the side imagine transducer.

I'm sure my issues are due to me mounting the transducer itself. I had a difficult time removing the old puck so was scared to epoxy and against all recommendations, I siliconed the new puck in place.

But with the switch I get readings while on plane and good sonar when not.