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Old 12th January 2011, 14:52   #1
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Default No voltage appearing

Hi all,
I had installed the music system in my Alto about seven years back. Some of the connections had become loose and I decided to re-wire the whole thing. I found that the battery wire that provides constant 12V is not existent at all. The wire is there but no voltage like there used to be previously. I checked the voltage across the battery with my multimeter and it shows about 12.3V.
The player works but it does not save radio stations, presets etc because there is no constant power source. Where do I start looking?

Thanks and regards,
Vivek
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Old 12th January 2011, 15:25   #2
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Default Re: No voltage appearing

Check the fuse first.
Else, run a wire (with a fuse) directly from the battery to the HU, problem solved.
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Old 12th January 2011, 15:31   #3
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Default Re: No voltage appearing

Hi Shankar,
Oh yes, that is the first thing I should have done. I suppose it will be in the fuse and relay box under the hood.
If I have to draw a new power wire from the battery, how much should the fuse rating be?
The other thing I noticed is that when I turn the ignition on to ACC position, even then I do not get a voltage at any point on the wiring harness under the dashboard. Does that indicate anything?

vivek

Last edited by Vivekphadnis : 12th January 2011 at 15:38.
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Old 12th January 2011, 19:23   #4
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Default Re: No voltage appearing

Yes it indicates the Fuse is blown. So first check that and then see if it is the ground, since ground would be common for direct and acc position. You can do this by grounding the multimeter wire on body bolt/screw.
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Old 12th January 2011, 20:40   #5
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Default Re: No voltage appearing

Since its evident you know how to use a multimeter. Follow the 12volt line. It can be a case of blown fuse.

BTW! like everybody suggested run a cable directly from the battery with a 10A fuse. It is much easier that way.
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Old 12th January 2011, 20:50   #6
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Default Re: No voltage appearing

I hope I have understood your question correctly.
You mean to say before re-wiring your system it was working properly and storing fm stations and all? And after wiring the system is working but not storing stations. Am I right?
Well if thats the case then you have wired your yellow and red wires wrong. Just interchange them and you will be good to go.
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Old 12th January 2011, 21:25   #7
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Default Re: No voltage appearing

Quote:
Originally Posted by deky View Post
I hope I have understood your question correctly.
You mean to say before re-wiring your system it was working properly and storing fm stations and all? And after wiring the system is working but not storing stations. Am I right?
Well if thats the case then you have wired your yellow and red wires wrong. Just interchange them and you will be good to go.
I tried interchanging the wires and the same problem persists. Then I checked with the multimeter and found no voltage at all (despite the ignition key position).
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Old 14th January 2011, 12:21   #8
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Default Re: No voltage appearing

I checked the fuses in the fuse and relay box under the hood and all of them are intact.

I could run a wire directly from the battery to the HU with a 10A fuse but I was just wondering what could be the problem and where I could check further.
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Old 14th January 2011, 13:06   #9
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Default Re: No voltage appearing

Did you check the ground wire (negative)??
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Old 14th January 2011, 18:34   #10
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Default Re: No voltage appearing

I tried grounding the negative lead of the multimeter to the body of the car and also with the ground wire under the dashboard. But I was not getting proper readings. Should I be checking the ground first?

Also, I checked all the fuses and they are okay.
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Old 14th January 2011, 19:00   #11
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Default Re: No voltage appearing

To check ground, touch the red lead of the multimeter to the wire that you're getting power from when the key is in ACC position (because you know that wire has power when you turn on the key) and touch the black lead of the multimeter to the ground wire in the same harness and you will get reading in your DMM. Do this with key at ACC.

Anyway i don't suspect the ground wire is bad since if the ground wire in the harness was bad your HU will not power up which its doing right now isn't it?

The HU needs only three wires to power up and function properly:
1) Battery (almost always Yellow)
2) ACC key on (almost always red)
3) Ground (almost always black)

In your case the HU is powering on when key on but not saving the settings, is it not?
So 2 is okay and 3 is okay. 1 is not ok. So you must've mistakenly tapped some other wire thinking its batt wire or the batt wire must be indeed kaput.

Are you sure you have tapped the correct batt wire? If not do this.
1) Turn the ignition key off
2) Disconnect the HU and its harness so that you can work better.
3) Set the DMM to read DC voltage
4) Push the black lead of the DMM into the ground wire pin of the harness. Let it remain there. Or ground the black lead of the DMM on a metal part of the body.
5) Use the red lead to probe other pins in the harness, you should get batt voltage reading at one of the pins. That is the batt wire.
6) None of the pins are showing any reading then something is indeed wrong with the wiring.
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Old 14th January 2011, 22:35   #12
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Default Re: No voltage appearing

Hi Sankar, thanks for the detailed reply. I will do a more thorough check this weekend. But I suspect a bad battery wire. You see, rats had chewed up the wires sometime back. Could have happened with this wire.
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Old 17th January 2011, 10:07   #13
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Default Re: No voltage appearing

I checked the wiring harness under the dashboard and the wire that has a constant 12V appearing had a loose connection. I did some soldering and rewiring. Problem solved. HU works properly now. Thanks to everyone for the help.

Vivek
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