It all sounds so simple: car radios are equipped with standardised connections enabling them to connect with loudspeakers and the car’s power supply. In case of incompatibility a suitable adapter enables the connection, at least in theory, as praxis sometimes shows something else.
Simple basic principle
The car radio is an electronic component subject to all laws of physics just like all other electric parts. Electronic component are also called “consumers“. These can be lamps, seat heating, auxiliary motors (electric window openers) or the sound system in the car.
The basic principle of electronics says current always runs in circuits. Every electric consumer should be installed in a closed circuitry. This consists of a power source with positive and negative pole and the accessory cables.
Simply said, all cables leading to the consumer are the outgoing cables and all wires leading back to the power supply the return cable.
Grounding saves cable
If every electric consumer in the car had its own separate circuitry, this would result in a cable spaghetti. Therefore a simple trick simplifying installation and making the car cheaper as well is used: The metal bodywork of the car is used as return lead. Both battery and generator are connected to the bodywork by a thick cable. Every consumer can create the return lead through connection with metal. This sounds ingenious and simple, though can lead to problems when installing car radios.
What power connections does the radio require?
This is not a dumb question at all, as a radio doesn’t require one but THREE connectors. Two apply to the car radio itself. The third one applies to the loudspeakers. Both connectors of the car radio are
– permanent positive
– ignition positive
The permanent positive maintains the radio’s memory functions. These are:
– the chosen menu language
– switching off the demo mode
– the channel settings
– the position of the CD or MP3-player at the moment when the car was turned off.
The ignition positive is the power supply for the normal operation of the car radio.
In the past these functions worked independently. Modern car radios require a safe connection with both power supplies to enable their functioning.
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The new car radio
There are plenty of reasons for a new car radio. The old one is broken or its functions are not up-to-date. Nowadays, speaker-phone functions and connections for MP3-players are standard. Purchasing an older second-hand car generally comes with an old radio without these functions.
Fortunately new car radios are supplied with adapters for connecting with the car’s power supply. Remarkably, its yellow and red cables are interrupted by a plug connector, not without reason.
Adequate tools are compulsory
For the installation of a new car radio you need:
1 wire stripper (mind the quality, no experiments with carpet knives)
1 set of cable terminals and connector blocks (lustre terminals)
1 pointed pliers
1 small, flat screwdriver (mind the quality, a cheap voltage indicator breaks down easily)
The universal tool for car radio installation is the multimeter. This appliance, available for less than £10, is practical and can help finding a fault in the wiring to prevent power errors. All you need to do now is act systematically.
The new car radio’s settings constantly change
This should be easy to repair: the fact that it works signifies it receives power. The permanent positive and the ignition positive have been exchanged. This is why the red and the yellow cable have a plug connector. Simply pull them out and cross-connect. The problem is solved and the radio functions as desired.
The new car radio is not functioning
Everything is connected but the radio doesn’t function. The following failures can occur:
Radio is dead
1. Check fuses
The cause of a power failure in the car is often a blown fuse. Check the fuse box. Don’t forget: right next to its plug connection the car radio has a flat fuse!
2. Further steps
If the radio doesn’t function despite fuses being intact, there is a problem with the power supply.
The first measure is installing the old radio by way of test. If it is functional, the basic operation of the cable harness is ok. In this case, there is a connection failure.
Now the multimeter comes in handy for retracing the connection. Important are the colours red, yellow and brown or black on the connector plugs of the car.
Tip: the feeler gauges have a cap insulating the shaft leaving only its tip free. By removing the cap the gauge can be inserted into the plug connectors.
The multimeter is set at 20 Volt direct current. Now the connector is checked for its power supply.
2.1 Remove ignition key
2.2 Put black gauge on brown or black cable and hold the red gauge against the yellow connector.
No reaction: yellow contact is not permanent positive or earth fault.
Indicating 12 Volt: yellow connector is permanent positive and grounding is present.
2.3 Put black gauge on brown or black cable and hold red gauge against red connector.
No reaction: red contact is not permanent positive or earth fault.
Indicating 12 Volt: red connector is permanent positive and grounding is present.
2.4 Switch on the ignition (without starting the engine)
Check the ignition positive by the same procedure.
2.5 Identifying earth fault
Connect the black gauge with the bodywork metal. Connect the red gauge with the yellow cable connectors and subsequently with the red cable. If power is present, earth cable rupture is probable.
If the plug has a valid grounding, connect it to the adapter. This enables you to check which cable is leading the earth connection. If the cable doesn’t go anywhere, the adapter’s connector should be adapted.
This is a meticulous work, requiring some skill. Principally, the adapter plug pins will fit another connection. This is why there are so many free connections for the power supply.
2.6 Switch on the light
If an earth connection is found on the connector, this is not necessarily conclusive. Deviating constructions by certain car manufacturers cause confusion.
Repeat the points 1 – 4 with LIGHTS ON. If a circuit is no longer found, the earth has a fault or isn’t properly wired for the radio.
Wiring a permanent positive
The simplest way of establishing a permanent positive is running a cable direct from the battery. Installing the wire requires some skill, but should create a clean solution, for which a 10 ampere fuse is required. Otherwise you run the risk of a cable fire in case of overvoltage.
The good news is that installing an earth connection is very simple. All you need is a long, black cable connected to a ring terminal. The terminal can be connected to any metal bodywork part.
Subsequently the black cable is connected to the black adapter cable by cutting it in half, insulating it and connecting it with a lustre terminal.
Installing an ignition positive
If no useful permanent positive is found on the cable harness, it can be obtained from another consumer. If this fault occurs, the ignition could be defective.
Instead of installing a new ignition you might look for the ignition plus elsewhere. For example the cigarette lighter or the 12-Volt car plug are suitable. Disassemble the component and access its electric connection.
Identify the right cable connection with help of the multimeter. The remaining cable – ideally red – is used to make a y-shaped connection. This is installed in the electric connector of the cigarette lighter. On the open end another cable can be installed to the adapter’s ignition positive connection. It would be perfect when this cable is equipped with a 10 ampere fuse.
Radio error message
Possibly, the new car radio would display an error message. And a typical message would be:
“Miswiring, Check Wiring then Power On”
In this case the radio doesn’t function at all and cannot be switched off either. The following has occurred:
The radio made an earth connection through its casing. This can happen if the installation frame or casing damaged the earth cable at installation. The radio should be disassembled and the earth connection checked. This should solve the error.
Installing a new car radio is not always as easy as manufacturers promise. By acting systematically with help of a little dexterity and the right tools, the most obstinate car radio can be installed in any car.
Foto: Hernando Sorzano, Hal_P, Mihancea Petru, Alefat, Tomasz Majchrowicz / shutterstock.com