Battery 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)

 

[lh333_34]

thank you all so much! problem found! the black one is not ground, but the white/black is ! I have been following the wrong information from another webpage, saying that the black one is ground !
I just tested the blue/yellow (the battery wire) and the white/black, the reading is 12V ! while the original radio is disconnected.

 

[lh333_34]

WOuld suggest you locate the exact diagram that refers to the model you have . This will make a huge difference !

Good on you and the rest of the members joined this discovery. The correct diagram solved the puzzle! Thanks to everyone.

 

[LukeD]

thank you all so much! problem found! the black one is not ground, but the white/black is ! I have been following the wrong information from another webpage, saying that the black one is ground !
I just tested the blue/yellow (the battery wire) and the white/black, the reading is 12V ! while the original radio is disconnected.

Have chased many a Cr hifi loom and they can be murder ! probably even worse these days .My way years ago was to skip the stock cables for power and fit fused 12v cable and a better ground . Made huge difference .Also when adding relays for "120w " front bulbs !!! The stock loom cable would never work well.

 

[LukeD]

Good on you and the rest of the members joined this discovery. The correct diagram solved the puzzle! Thanks to everyone.

Its what we do... we spread the love .

 

[DPG]

Well spotted @AvoMk8 !

More words here.