Positive earth, Negative earth? How to tell?

[Lowriderlad]

Hi there just about to fit a radio in my morris and I need some advice with the wiring. The three wires that I need to connect are...
Battery 12v(+) / Yellow
ACC+ / Red
Ground / Black

Could you please advise how to hook these up and how to tell wether its +/- Earth. Thanks.

[Alec]

Hello Lowriderlad,

you need to be sure your car battery is connected with the negative pole to earth. If your car has an alternator then it's probably that already. If it's a dynamo, you'll need to change it.

I'm not so familiar with radios, but I think the battery will be fed from the ignition supply and the Acc directly from a continually live source. If you look at your fuse block, one fuse (Purple wires) is always live and the other (White and green wires) is live with the ignition on only.

Alec

[Lowriderlad]

So in theory could I connect both the Acc and 12v Battery wires directly to the live of the battery? That way the stereo can be used when the ignition is off and it saves me from removing the speedo to gain access to the ignition loom. And the ground just goes to an area of metalwork on the car. Ps. I have checked and the negative pole of the battery goes stright to a bolt in the engine bay.

[alex_holden]

Yes, but don't forget to put an inline fuse as close as possible to where it connects to the battery, and fit a grommet to the hole where the wires pass through the bulkhead.

Normally the battery wire goes to a permanent live, and the accessory wire goes to an ignition switched live (modern cars have an 'accessory' position on the ignition switch which lets you listen to the radio etc. with the engine off).

[Alec]

Hello Lowriderlad,

the reason I mentioned the fuses in my first reply was so that you connected there, rather than the battery.If you want it on permanently then just connect both positives to the always live.

Alec

[Nuffles]

So in theory could I connect both the Acc and 12v Battery wires directly to the live of the battery? That way the stereo can be used when the ignition is off and it saves me from removing the speedo to gain access to the ignition loom. And the ground just goes to an area of metalwork on the car. Ps. I have checked and the negative pole of the battery goes stright to a bolt in the engine bay.

If you do this the radio will be 'on standby' all the time and will run your battery down pretty much overnight. If you don't mind about the radio not being ignition controlled simply hook up the 12V battery wire, this will allow you to turn it on and when you turn it off it will be properly off. I had mine set up like this for a while but ultimately found it very annoying having to open my glove compartment to turn the radio off every time I stopped. Wiring the acc wire into the ignition takes a little more time but it's worth it.

[Lowriderlad]

Hi there, How do I know which wire supplies the feed from the ignition for the ACC wire, and how to I access the ignition (In detail)? Thanks guys you have been so helpfull.

[alex_holden]

Hi there, How do I know which wire supplies the feed from the ignition for the ACC wire, and how to I access the ignition (In detail)? Thanks guys you have been so helpfull.

Look for a four way bullet connector with dark green wires going into it and a spare socket you can plug your cable into. The blue crimp-on bullet plugs work but they are a bit big and you have to crimp them well or the wire can pull out - the solder-on 'nipples' are better if you know your way around a soldering iron. Alternatively you could run a new wire from the fusebox - connect your wire to the place where the dark green wires attach.