Instructables

How do I fix my car stereo ground wire?

I installed my new stereo and it won't work. The fix-it hotline told me to touch the ground wire to the negative batt. terminal, and the red and yellow wires to the positive terminal. The stereo worked, meaning the ground wire coming from the dash is probably bad.?

or maybe its the 12v wire and not the ground thats damaged, did you check the fuse in the car fusebox to make sure you didnt blow it on installation, have you metered the 12v coming from the car wiring loom into the red and yellow wires on the stereo to make sure the ignition key switched the power on to the correct wires?

your car aerial connector also acts as a ground, so if youve got the aerial plugged in and your stereo still doesnt work i would suspect a 12v fault
robjob1918 (author)  whitebakecase4 years ago
checked fuse box. its good. didn't meter. is the 12v wire the red marked acc/ ignition? i touched it to metal and it sparked, so i know it's live. what is the aerial wire? also note that the rear defrost now doesn't work. also noticed changes in the way my interior light works. i hope i'm not screwed.

You will need a meter, or some form of checking for 12v eg a LED with a series resistor, or some sort of 12v buzzer etc.  And dont be tempted to test by sparking wires to ground, you might melt wires in your loom!

The wiring loom colours and connectors on the car's loom can vary, in most cases its far easier to purchase a loom adapter which converts the car's existing plugs to suit the connector on the radio.  This is unless your radio or your car loom already has the plugs hacked off and youve been left with just wire ends.

From the back of the radio there will be one group of wires for the speakers, and another group of wires dealing with things like power antenna and ignition switch.  Some radios also have outputs that wire to in-car hands free mobile mounts to mute the radio when the phone rings.  Theres a whole array of auxillary controls on most modern radios but your installation manual will tell you what wires are for what.

The aerial plug is the one which comes from the car aerial, behind the car dashboard and appears inside the radio slot with the rest of the radio loom.  Its a fairly thick black wire with a shielded metal plug, and there will be an aerial connection point that it mates with on the back of the radio,

You will need to locate 3 important wires to make the radio switch on.  These are the earth wire, the ignition wire, and the permanent 12v wire.  Car radios tend to use a red and yellow wire for the permanent 12v, and a black wire for 0v (earth), but again the radio manual will be more specific.
These same 3 wires will need locating on the car loom now, and I'm going to assume that you have a meter of some description that can read DC voltage in the range of 0-20VDC. 
You could use a buzzer or the like, but with a meter you can check for level and not just presence.  It can be difficult for example to distinguish the difference in an LED intensity from 10v to say 6v, but this difference can have a big impact on the way your radio will work.

Turn the ignition key in the car so that the dashboard lights come on, you dont need to start the engine.

Locate a good earthing point and press your black meter probe onto it. 
Good earthing points are sometimes found under the gear lever gaiter, in the door hinges, etc, just something nearby so your meter leads will reach without straining.

Now take your red meter probe and touch it to the bare metal end of each wire from the car wiring loom in turn, and observe the voltage on the meter.  Two of the wires should give you a reading of between 10-14 volts.  If you don't find at least one showing 10-14 volts, recheck the fuses in the car fusebox properly with a meter, as it is possible for a fuse wire to melt without blowing, but cause a high resistance and thus lower volts.

So, once you have located these two wires (and yes you may find they are red and yellow, but if not dont worry), now you need to find which is the ignition switched wire.  First, turn off the ignition key, and remove it fully.  Keep your black meter probe on the earth point, and with your red probe now recheck the two wires you have just identified.  One of the wires will read at 10-14 volts, and the other will now read 0 volts, or around that.
The wire which has lost power is known as the ignition feed and the wire which has retained power is the battery or permanent positive 12v wire.  These must be connected to the corresponding wires on the back of the radio,

Ok, so now to locate the correct earth in the loom.  Sure, the aerial plug might make a good earth substitute, but using this as an earth for the radio has caused me problems in the past with interference, and the coaxial cable that is used for the aerial connection is simply not designed to cope with the power demands of some modern radios.  Its best to use the correct earth wire in the loom as its generally thicker and able to deliver current to the radio much better.
Hold your red probe onto the wire you have identified as permanent 12v, and now use your black probe to check each of the other wires from the car loom, you should find one wire that shows a reading of 10-14 volts, and it may be much thicker than the others.  Common colours for earth vary, brown, black, grey, dark colours are popular with manufacturers, but dont use that as a general standard, you should always meter to get things right.

Now you need to connect the car earth wire to the radio earth.  Always use equivalent or bigger gauge of cable.  The earth point on the radio might be a dedicated wire or you might have to clamp the wire under a bolt on the radio casing, refer to the radio manual for clarity.

If everything has gone smoothly, your radio should now switch on when the car ignition is on, and off when the ignition is off, and if the radio has a removable front plate you might find a red security LED flashing behind it.
If you program any radio stations, these settings should be retained when the radio is powered off, and you shouldnt lose any equaliser or display settings.  If you do, theres a problem with the permanent 12v wire.

As for the courtesy light and rear screen problem, these may be related depending on the configuration of your cars fusebox.  Often the radio fuse will also feed things like dashboard lights, and other low current devices.  If it is the case that the fuse has gone high resistance, voltage levels to all the other connected devices will drop and some may start to misbehave or stop working completely.  Recheck the relevant fuses within your fusebox!
Meter both metal connectors on the fuse and you should see a resistance of less than 10 ohms or so.

Further than that, it could be completely coincidental and unrelated, or worst case you might have caused some melt damage in your cars loom by creating sparks!

Hope this helps





 

gverma22 years ago
hey any one can help me as i just install a new head unit in my car, every thing is good but when i switched off my ignition & lock my car, then again unlock the car start the ignition my all setting on head unit turn again to factory settings, please some can help
Sounds like it doesn't it. Take a nice big fat wire and clamp it under a good heavy bolt head on clean metal.