Wylietunes

Dont misunderstand my post. Im not say dont mount the rev-10, I just would not run them next to an 8" coaxial. You will hardly know the smaller speaker is there. Id pull the existing coaxials and go with just the larger 10" HLCD.

Not blasphemous to mix brands, but i dont suggest mixing types. The 10" HLCD is going to totally dominate a smaller 8" dome tweeter coaxial. To the point of almost not being worth the battery juice to power the amp for the coaxials.

Sounds like they are on the same switch, a ON/OFF/ON? One reason could be that above gunwale accent lighting typically falls outside of proper navigation lighting, so having them on, especially under way, can result in a ticket. Depending on the switch style, it may be possible to wire them so all are on one position, then cabin lights on only, in 2nd position. A dedicated light for each would allow for the most flexibility.

I think they offer 2 https://www.jlaudio.com/collections/marine-audio-source-units-mediamaster/products/mediamaster-mmr-40-marine-audio-remote-controller-99910

Which remote is the OEM option? Knowing this, id call JL and aske them how their remote works. The Fusion unit only works with Fusion media units, and only a select few.

Is a 2018 not using the Indmar Raptor? If so, its a partially closed cooling engine isnt it, so you would not be draining the engine, just the exhaust and raw water intake portion. With that said, its best to drain all the water first. Marine/RV A/F is designed for use at 100%. Diluting into a system full of water, will raise its freeze point. This usually does not take long, especially the 2nd season. It also does not require any more A/F then the system hold. No need to keep pumping it in until you see a color change. Even then, of you do a proper drain, A/F is not needed. Shops

One volt gauge and a DPDT switch will allow you to see the voltage of both batteries.

If both batteries are fully charged, id suspect a bad cable on the #1 or a bad switch. Position 2 is mechanically the same as position 1, just electrically pulling from a different battery. So if the boat works normal on #2 and both batteries are fully charged, bad cable or switch. With that switch type EVERY load (*) should go through the common output post of the switch. MB tended to wire things like the amp, direct to battery #2. * the exception would be the auto bilge wire, which should be wired battery direct.

If original, a 2013 is likely not wired in the most ideal manor. With that said, it sounds like you have a dead battery. Break out a volt meter and test them both.

So you've eliminated everything upstream of the amp. odds are slim to zero the noise is entering in the speaker wires.

Are they power by their own amp? Technically, this can be one half of a 4 chnl amp thats also powering the main cabin. Do they have their own pre-amp signal supply or is it shared with all the cabin speakers? This starts to isolate the issue.

The 4 full range chnls of the javelin deliver 150W rms x 4 @ 2 ohm, so thats 75W rms to each speaker with a pair in parallel p/chnl. I do not think you have a too much power issue, but maybe a cross-over issue. Id start with tuning.

Are all 4 the same size and type? Are the 2 you want to address, wired together on one channel or are they in parallel with the other pair? What is your goal for the 2?

Diagnose the failed component and order a replacement part. All three audio components are serviceable and usually in stock at the factory.

I guess a transom remote is now an option as well.