Fitting a DAB car radio. Do I need an earth?

[neil_s]

If your radio has a security code, you will need to connect the permanent +12v direct to the battery, otherwise you will need to type in the code every time you switch on.

 

[Refueler]

Very often it is the permanent supply which supplies the main power, you can get caught out thinking it's only a milliamp or two to retain the tuning memory.

????

I've fitted many radios to my cars and boats over the years and the permanent supply has ALWAYS been the Memory Retention supply .....
Main power for actual radio use has been the switched supply.

 

[john_morris_uk]

????

I've fitted many radios to my cars and boats over the years and the permanent supply has ALWAYS been the Memory Retention supply .....
Main power for actual radio use has been the switched supply.

Agreed. No question.

 

[lw395]

????

I've fitted many radios to my cars and boats over the years and the permanent supply has ALWAYS been the Memory Retention supply .....
Main power for actual radio use has been the switched supply.

That's what I thought, until I was asked to sort out a radio on a mate's boat, and the permanent supply blew a 5A fuse.
I forget what make the radio was.

 

[prv]

I've fitted many radios to my cars and boats over the years and the permanent supply has ALWAYS been the Memory Retention supply .....
Main power for actual radio use has been the switched supply.

Is that from the manual? Because if the 'permanent supply" wiring happens to be sufficient to run the radio (which isn't all that demanding) without blowing a fuse, I can't see how else you'd tell the difference.

(I haven't messed about with car stereos since I was a teenager, but I've certainly encountered other equipment where the "switched supply" is just a signal to turn on.)

Pete

 

[[163233]]

That's what I thought, until I was asked to sort out a radio on a mate's boat, and the permanent supply blew a 5A fuse.
I forget what make the radio was.

When the radio was turned off?!?

That'd be a right bugger in a car, the battery would be dead in about 10 hours.

 

[Refueler]

Is that from the manual? Because if the 'permanent supply" wiring happens to be sufficient to run the radio (which isn't all that demanding) without blowing a fuse, I can't see how else you'd tell the difference.

(I haven't messed about with car stereos since I was a teenager, but I've certainly encountered other equipment where the "switched supply" is just a signal to turn on.)

Pete

If I find the installation sheet from the last radio I fitted - I shall gladly scan and upload.

Your question is actually easily answered as to which. If you connect both wires and program the radio. Now remove one +ve wire ... wait a couple of minutes ... then try switch on. You will either have nothing happen (that means its the main power disconnected) or radio will come on and because of letting the system decay - most likely you will have lost all programming (because that's the Memory wire disconnected).

Ask yourself why would MAIN power be permanent live ?

 

[Refueler]

Maybe try reading this :

How to Identify OEM Car Stereo Wires

Scroll down a bit ad it explains the different wires .....

Check for Power
Whether you&'re dealing with a car stereo, a receiver, or a tuner, most head units have two or three power inputs. One power input is hot all the time, and it’s used for ‘memory keep-alive’ functions like presets and the clock. The other is only hot when the ignition key is on, which prevents the radio from being left on after you've taken the key out. In cases where a vehicle has a third power wire, it is used for a dimmer function that's tied to the headlights and the dash light dimmer switch.

The first power you'll want to check for is the constant 12V wire, so set your multimeter to the appropriate scale, connect the ground lead to a known good ground, and touch the other lead to each wire in the speaker wire. When you find one that shows approximately 12V, you have found the constant 12V wire, which is also referred to as the memory wire. Most aftermarket head units will use a yellow wire for this.

and just to show its not a one off site :

How to install a car stereo

Scroll down again and we find :

Power wires
Usually, it is best to make all of the new stereo's wiring connections via the wiring harness, but if you have to make a direct power connection, you'll need to know the difference between "switched" and "constant" power:

• A switched power source is only on when the ignition is keyed. Connect your new stereo's main (switched) power lead – usually a red wire – to a switched power source, so that the stereo will turn off when you turn off the car, and not drain your vehicle's battery.
• A constant power source is always on. Connect your new stereo's memory lead – usually a yellow wire – to a constant power source, so that you don't lose your radio station presets, tone control presets, and clock settings every time you turn off the vehicle.

I rest my case m'lud !

 

[anoccasionalyachtsman]

If I find the installation sheet from the last radio I fitted - I shall gladly scan and upload.

Your question is actually easily answered as to which. If you connect both wires and program the radio. Now remove one +ve wire ... wait a couple of minutes ... then try switch on. You will either have nothing happen (that means its the main power disconnected) or radio will come on and because of letting the system decay - most likely you will have lost all programming (because that's the Memory wire disconnected).

Ask yourself why would MAIN power be permanent live ?

I must admit that I'd assumed (there it is...) that the red (ignition connection) was the proper power supply, mainly because it was errm, red. Yellow isn't a proper colour for main power, right? But now I think about it there's no obvious reason for it to be that way round, and I can also see that the yellow is more likely to end up connected to something that can safely deliver several amps.

 

[Refueler]

I must admit that I'd assumed (there it is...) that the red (ignition connection) was the proper power supply, mainly because it was errm, red. Yellow isn't a proper colour for main power, right? But now I think about it there's no obvious reason for it to be that way round, and I can also see that the yellow is more likely to end up connected to something that can safely deliver several amps.

If you read the links I gave in another post later .... red is the switched main power and yellow is usually the constant memory power lead.

 

[anoccasionalyachtsman]

If you read the links I gave in another post later .... red is the switched main power and yellow is usually the constant memory power lead.

That's what I said.

 

[Refueler]

Is that from the manual? Because if the 'permanent supply" wiring happens to be sufficient to run the radio (which isn't all that demanding) without blowing a fuse, I can't see how else you'd tell the difference.

(I haven't messed about with car stereos since I was a teenager, but I've certainly encountered other equipment where the "switched supply" is just a signal to turn on.)

Pete

Actually there are a number of radios that require a separate fused wire direct to battery instead of through the fuse panel because of the power rating ...

Don't believe me ?

How to install a car stereo

To my rescue again .....

Power wires
Usually, it is best to make all of the new stereo's wiring connections via the wiring harness, but if you have to make a direct power connection, you'll need to know the difference between "switched" and "constant" power:

• A switched power source is only on when the ignition is keyed. Connect your new stereo's main (switched) power lead – usually a red wire – to a switched power source, so that the stereo will turn off when you turn off the car, and not drain your vehicle's battery.
• A constant power source is always on. Connect your new stereo's memory lead – usually a yellow wire – to a constant power source, so that you don't lose your radio station presets, tone control presets, and clock settings every time you turn off the vehicle.

Although rare, a few high-powered stereos require you to make a direct constant power connection at the positive terminal of your vehicle's battery. This requires a heavier gauge power wire, an in-line fuse (usually included), and a ring terminal to connect the power wire to the battery clamp. You will have to route the power wire to the battery location, which is often through the vehicle firewall and into the engine compartment in order to make the connection at the battery.

 

[Refueler]

That's what I said.

Sorry ... my post comes across a bit blunt and rude there .. not intended. I was agreeing with your assessment.

Sorry.

 

[Refueler]

That's what I thought, until I was asked to sort out a radio on a mate's boat, and the permanent supply blew a 5A fuse.
I forget what make the radio was.

Obviously you had the wires swapped over ....

 

[PaulRainbow]

So if there’s two positives (permanent and switched), should they be connected together and put on single fuse? And what size fuse?
I’m just about to start installing mine.

Two options:

1) Permanent positive to the battery, switched positive to the isolator switch or busbar. Both cables need to be fused, close to the supply. The radio will go off when you turn the isolator off, but the clock, programmed stations and other settings will be retained. There will be a small current draw all of the time.

2) Run a single cable from the isolator or busbar to the radio, fused close to the source. Close to the radio, connect both positives to the single wire. When turned off the clock and all settings will be lost. There will be no current draw whilst the isolator is off.

 

[tmtracey]

Thanks Paul.

There is a 10A blade fuse in the back of the unit, but I'll add another inline fuse. Should this be 10A too?
Based on a previous thread, I was going to use a 500 mA fuse on the constant supply.

 

[tmtracey]

I'm planning to use bluetooth speakers with it.

 

[PaulRainbow]

Thanks Paul.

There is a 10A blade fuse in the back of the unit, but I'll add another inline fuse. Should this be 10A too?
Based on a previous thread, I was going to use a 500 mA fuse on the constant supply.

The fuse in the radio is to protect the radio. You fuse the cables at source to protect the cables themselves. The fitting instructions for the radio should specify fuse ratings.

 

[lw395]

When the radio was turned off?!?

That'd be a right bugger in a car, the battery would be dead in about 10 hours.

No, when we turned it up to test it.
Found some blurb for a Pioneer radio, wants a 15A fuse in the 'permanent' supply, that's a shitload of memory retention.
Not saying all radios are the same.
There is some ambiguity in the pin definitions of the DIN connectors that many radios/vehicles use.

 

[[163233]]

No, when we turned it up to test it.
Found some blurb for a Pioneer radio, wants a 15A fuse in the 'permanent' supply, that's a shitload of memory retention.
Not saying all radios are the same.
There is some ambiguity in the pin definitions of the DIN connectors that many radios/vehicles use.

Ah, I see what you mean. I was thinking about why you would want a permanent supply that wasn't switched.

Personally I feel that non-essential items on boats should always have a breaker to turn them off completely, which would mean picking the head unit carefully for stuff like PINs, clocks and my personal bugbear - demo modes.