General Wiring Question

[Ray]

Before I bought it my boat had a car type radio wich the previous owner removed. I have found the wiring to it which was cut off with pliers and taped off.

I will either fit a new radio/cd or simply use the wiring to fit a new accessory socket but I could do with some help clarifying the wires (leaving aside the speaker and aerial which are easily identified)

From the radio to a panel on/off switch is a red wire.

Back from the switch back to the fuse is also a red wire.

From the same side of the fuse a brown wire leads back to the radio

From the radio to the main board marked "battery negative" is a blue wire.

Depending on what I fit the switch is not a must have, although probably useful.

So I have 3 wires and in my (limited) experience most accessories etc. have 2 terminals. How would I use these wires please?

[JanetAnne]

Sounds like you have two live wires. One will be the normal live and the second an AUX live that keeps the radios memory when you turn the unit off. 

In a car the first live would be from  the ignition switch so the radio turns off when you turn off the key and the second wire would be a permanent live direct from the battery (well, fuse box) to keep the memory so the radio comes on with all your chosen settings still in place.

[JanetAnne]

Your replacement unit will confirm this in its wiring diagram.

However, to replicate the same on a boat the first live could be switched as you mention but the second memory wire should go to the live side of your isolator switch so that it remains on when the batteries are turned off. 

Of course you can use it as it is currently wired and just retune the unit every time but the unit will require both live wires to be live to work.

[Ray]

That sounds like the perfect answer, thank you very much. Whatever I fit I'd prefer it to be definitely off so I can ignore the keep alive one... trial and error should identify it!

[dnks34]

You need to know which of the 2 live wires is the permenant live and which is the switched, but being a boat theres a chance they may both be on permenant. 

Also if using the old wiring to feed a 12v socket instead of the radio you will need to decide if the feed is up to the job of powering whatever you intend to plug in to it.  

If its low power items like chargers I imagine it will be ok but heavy duty spotlights or vhf radios etc could require a more heavy duty supply.

[Ray]

Oops cross posted, sorry Yes I see what you mean about requiring both live wires.

[Ray]

Thanks dnks34, I was thinking phone charger.

[dnks34]

FM radio feeds are usually at least 10amp so a phone charger should’nt be an issue

[dnks34]

With it being a boat I would rather have it that even the 12v (permenant) memory feed for the radio goes to the switched side of the isolator but thats just my preference as rarely would i turn my isolators off but when I did I wouldnt want the radio to keep drawing power if the boat might not be being used for a while. 

[Ray]

That's what I was thinking, as my better half just said a radio/cd would be nice.

Sorry for complete newbie question but how am I sure that I'm on the switched side of the isolater? Do I simply join both my live wires in effect making one?

[JanetAnne]

If it was me putting a charger socket in I would keep the red wire 'switched' live and remove the second (brown?) live completely back to the fuse.

By the way, a car radio memory uses just mili- amps and would probably run a 110 battery flat in about 9 years 

[Ray]

9 years! Time for an extra pint then! 

Thanks again for the advice, I have a good idea how to proceed now. Time to look at radio/cd/mp3/Bluetooth/DAB thingys! 

[dnks34]

you could put the 2 lives together (aslong as they definately are live!) but if you do that and your 12v socket still stayed on when you turned the main isolator off your not really any the wiser! 

As JA says you will only want to use one live for an accessory socket the second live is only required for radio to keep the tuning memory set.

If it were me I would want a 12v socket to stay live independent of ignition (key) but go off with the isolator but it does depend on your installation and your requirements.

 

[Ray]

That makes sense, thank you both... this sort of advice is invaluable, learning how to do things and doing them yourself is so much more interesting and rewarding than getting someone else to do it ?

[StillCruising]

To find the switched & permanent wire you could use a light bulb with wires attached with one side to a known negative and the other to each of the positives  in turn, switching the ignition on and off. The one that makes the light go on and off will be the switched live, the other will be the permanent feed. Better yet get yourself one of those cheep digital multimeters from fleabay or local cheepy shop for the testing and keep it on board for future use. Even after nine years of ownership I'm still trying to fathom out where some of the wires feed from and end up. That said it probably doesn't help that there has obviously been a lot of additions (and subtractions) to the original wiring over the years when the boat was on the French canals which did not conform to any sort of convention.

The current taken from the live feed is a few milliamps and would not drain your battery I would make sure that there is a fuse in the line though. Personally I don't like permanent feeds on a boat and  the only thing that is live on Miss Lisa when the isolator is switched off is the bilge pump (through a fuse).

[dnks34]

I agree the bilge pump is the only thing Ive ever had wired to the constant side of the Isolator but each to their own!

[dnks34]

Ive got one of these:

https://www.toolstation.com/shop/Automotive/d60/Automotive+Electrical+Testers/sd3263/Car+Light+Tester/p84459

and one of these

https://www.screwfix.com/p/lap-mas830b-digital-multimeter-600v/75337

They make life easier! 

 

[Ray]

Good idea about the meter.. my bilge pump by the way is only live when the isolater switch is on, maybe something else I should look at.

[JanetAnne]

We tend to have a separate 4 way permanently live fuse box for when the isolators are off.  This runs bilge pumps (we are talking woodies here so bilge pumps can be your best friend) a switched cockpit entry light for late night arrivals and the last fuse runs the alarm as well as radio and clock memories. This fuse box is separate to the normal isolator controlled main.fuse panel and is marked as such

[Ray]

Sounds like a very good set up, a long way beyond my abilities (so far) No woody either (so far) 

[dnks34]

One thing I will say about an Isolator to a newbie is dont assume that its been fitted on the positive feed.

Im not sure what way is best practice but whilst doing some work on a boat we once had I couldnt understand why a new piece of equipment wouldnt work no matter what I did until  I realised the Isolator i had wired from was on the Negative feed.

Now rightly or wrongly I assumed an Isolator would be put in the positive feed but my advice is If your boat is an ex hire boat never assume anything!!

[Ray]

Good tip, thank you.