What is best way to replace KTS-300mr on boat with newer model

You are drifting? In current? Then your relative speed in relation to the current is approximately zero.

if its an older motor its probably 2 stroke you add oil if newer it could be 4 stroke best bet get serial number and call dealer of that brand they can tell you

The serial number is so short it makes me think it's a 1958 model but newer models with 9 digits or more use the last two numbers as the year model which would make it a 1980. You can verify this by either going to NADA.com and looking at the different model names and numbers or just calling your state's boater registration department and asking them.

(http://inform3.kenwoodusa.com/manuals%5CKTSMP400MR.pdf )
Here's a link to manual and wiring on page 30 on the PDF file.
Yellow is constant power from battery, for memory etc. Red should be to switched source.If need be, you can connect both to battery, but remember, you'll have constant power draw on battery when stereo left on but switch turned off, and will draw battery down, if you forget to shut it off, and leave the boat. Speaker negatives to black should work but I would advise hooking my 2 right and 2 left + speaker wires from stereo together, then to one of the speaker positives,right or left for better sound. Fronts will usually supply higher ( high and mid range), and rears will supply lower sounds (woofer) Joining them together will give better sound usually, when only using 2 speakers, on a 4 speaker stereo. You may want to test with them joined and not, to see what sound you like better.

you need to firstly trace the speaker wires to the unit to make sure there connected first. if they are then its a job for a car audio expert ( if there is such a thing) if the unit is connected to correctly to the speakers then there is an internal fault ..

When you connect multiple speakers to one channel it drops the impedance. A radio is designed to play at 4 ohms which would generally be one speaker. When you connect two speakers to one channel it drops to a 2 ohm load which can be fatal for a radio but not always

Hello plainolelow,

"CALL" is displayed whenever a telephone call is received.

This is controlled by the brown wire from the wiring harness, and is activated when your telephone system or bluetooth device adapter detects an incoming ring. Activation is a "ground" on the lead. If you do not have a telephone or bluetooth adapter attached, the wire is probably coming into contact with some other wire or metal that is causing it to be momentarily grounded.

Hope this helps.

I don't have a solution, but did you ever get this working again? I'm having the same issue. Thanks

the tact switches have failed to the vol up and down switches. This is common as they do the most work. replacing the switches will fix it