Car radios 2 (installation)

[Metabarca]

I'm in the process of plonking a car radio/CD in my boat now, but I'm a real no-hoper when it comes to electrics. Clearly I can't earth the thing by bolting the associated cable to the hull (I ain't THAT innocent!). What about polarity? Also, there seems to be more than one power cable. WhadoIdo? Can anyone of superior intelligence help?
Buon anno a tutti!
Or if you prefer, Srecno novo leto!

 

[Strathglass]

Polarity - it is highly probable that both your boat and the CD player are negative earth.

Two positive supply leads - one will be the main supply to the unit, in a car this would normally be switched on through the ignition switch.
You would not necessary want to do this on a boat.

The second lead will be the always on supply this is the one which feeds the circuit which stores the preset stations it may also be the one which and theft software key and unless power is maintained on this line the security code would have to be keyed in each time the radio was switched on.

The easiest, but not the most correct thing, would be to take both leads (thro a suitable fuse) direct to the battery.
The other way would be to take the always on line (fused) direct to the battery and the switched line (fused) to the battery supply after the isolation switch.

Earth - you may get a suitable earth connection without doing anything through the negative lead.

 

[Metabarca]

Thanks for the exhaustive reply; I'll try it out this weekend!

 

[snowleopard]

aerial...

stuck about 6ft of wire down the centre of the aerial socket & taped it up behind the hear lining. worked a treat!