Car radio battery wire zero voltage ! but original car radio is working when connected. Why?!

[lh333_34]

Hi everyone
I am new in this forum and this is my first thread.

Car model: Toyota echo 2004 sedan.

I used a multimeter to test the car radio battery wire ( blue/yellow) when it was disconnected from the car radio, its reading was 0v. ( as shown in photo 1 ) before and after ignition, isn't it supposed to have constant 12v even being disconnected from the original radio?

but after I connected the original radio to the harness, its reading was 12v before the ignition (as shown in photo 2) , and 12v after the ignition ( as shown in photo 3) .

I would like to find out why it is like this?

When I tried to connect an after market radio to the harness, the battery wire still read zero before and after ignition, because of this, the after market radio could not be powered up. ( I tested it on direct 12v power supply, the after market radio was working) .

I am looking forward to getting some advice from experienced members on this forum.

Thanks in advance.

photo 1 ( harness disconnected from the original car radio )


photo 2 ( 12v when original radio connected to the harness, before the ignition)




photo 3 ( 12v when original radio connected to the harness, after the ignition)

 

[littlespark]

Without knowing exactly cable colours of the vehicle and the radios… and the plug/socket combinations may not be standard.

Radios can have 2 x 12v lines. One direct from battery to keep radio tuning memory’s etc and one from ignition.

I put an after market Chinese special into my daughters 2011 picanto. Perfect fit socket, but the 2 x 12v lines were wrong way round.

 

[lh333_34]

Without knowing exactly cable colours of the vehicle and the radios… and the plug/socket combinations may not be standard.

Radios can have 2 x 12v lines. One direct from battery to keep radio tuning memory’s etc and one from ignition.

I put an after market Chinese special into my daughters 2011 picanto. Perfect fit socket, but the 2 x 12v lines were wrong way round.

I tested the wires with the multimeter, while the original car radio is connected to the harness.
The (blue/yellow) is the constant battery wire, it has constant 12V before and after ignition.
The gray wire next to the battery wire (blue/yellow) is the car accessory wire, it has 0v before ignition, and 12v after ignition.
When the original car radio is disconnected from the harness, The battery wire (blue/yellow), and the accessory wire ( gray) has 0v before and after ignition.

All wires are determined correctly, my question is about the voltage of the battery wire (blue/yellow), which is supposed to has constant 12V, whether or not the original car radio is connected to it. But in reality, it is not as what it is supposed to be. When the original car radio is disconnected from the harness, the battery wire has 0V !!!! before and after ignition. ----- why? my question is about this.


Littlespark, I appreciate your reply and input.

 

[DPG]

If the permanent live wire is dead with the radio disconnected then something is wrong. Check at the appropriate fuse.

The fact that it becomes live when the radio is connected is irrelevant, as the radio may well cause it to pull up to 12V.

 

[lh333_34]

My question can be simplified as above diagram shows

 

[DPG]

View attachment 107446

My question can be simplified as above diagram shows

Post #4. Something is wrong with your permanent live.

 

[lh333_34]

The car has neither electrical issues , nor audio issues at all. The original car radio works perfectly. I just realized the above mentioned weird symptom ---- 0 V on the battery wire ( constant 12v ) and the accessory wire ( ignition 12V ) while the original radio was disconnected from the harness. I suspect this could have something to do with the radio security? ( but the original radio has no security code set for it.)

 

[DPG]

The car has neither electrical issues , nor audio issues at all. The original car radio works perfectly. I just realized the above mentioned weird symptom ---- 0 V on the battery wire ( constant 12v ) and the accessory wire ( ignition 12V ) while the original radio is disconnected from the harness. I suspect this could have something to do with the radio security?

So it remembers any stored settings, etc ? There's no actual problem?

Must admit I'm intrigued. It's fairly basic stuff this

 

[lh333_34]

My logic tells me that if there is something wrong with the original wiring ( eg. somewhere in the wiring is damaged or a fuse is blown ) the constant battery wire and the accessory wire should not work either with the original car radio or the after market one.
The weird thing is : when the original car radio is connected, all voltages on the wires are normal as we expect. But when the original car radio is disconnected, No voltage on all wires. What would be the reason causing this???

 

[Avo Mk8]

Is it possible that the circuit you think exists, that you have drawn, is not exactly how it is?

From a quick look (which may be wrong!) it appears you are measuring between the +12 V supply and the aerial motor connection?

 

[mainline]

Is there only the one plug in use ?


Blue/yellow should be constant 12v
grey should be switched 12v
black - ground -

pink - illumination
violet - dimmer


The other plug should be speakers ?

front spks

left + pink
left - purple

right + green
right - blue


rear spks

left + black
left - yellow

right + red
right - white


Do these colours make sense on your radio ?

Also would be better to use a test lamp rather than a multi meter.

 

[LukeD]

Is there only the one plug in used ?

THis question makes sense ..As the speakers are not all been fed from ONE plug .If the diagram is correct . you are only wanting to test 1-2-3

 

[DPG]

THis question makes sense ..As the speakers are not all been fed from ONE plug .If the diagram is correct . you are only wanting to test 1-2-3

Normally the live/switched live/electric antenna are on one plug and the speakers are on the other. OP, can you clarify

 

[lh333_34]

The red probe is on the battery wire (blue/yellow) . The black probe is on the ground wire (black one).

 

[DPG]

Just seen the connection pin out. OP, can you confirm exactly what the problem/symptoms are.