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Hands free car kit not powering up

A couple of weeks ago I bought a Sony Ericssson car kit from someone I know. First time I connected it up it worked for 10 minutes then when I turned the car off and restarted it - nothing.

Thinking I might have pulled a wire loose somehow I removed the whole thing and retested it and it's been refusing to play nicely ever since.

To power it , there are three wires - Black for earth - Red for permanent

12v and Blue for ignition sense that needs to be connected to a switched 12v supply.

I reconnected the power wires to the fuse box (once fuse for switched 12v and another for permanent 12v plus a handy earth) and checked that I was getting the correct voltages at the connector where it goes into the car kit.

Plugged it together , switched on the ignition and nothing happened - no signs of life. Rechecked everything - definitely getting 12v at the connector where it goes into the car kit but it won't work.

I removed it all as I'd run out of time and then tried again a couple of days later with the same results. Thinking this was very odd I got my multimeter out again and measured the volatage that I was getting at the fuse with it connected to the car kit , and with the ignition off I was getting 12v. If I turned the ignition on so that the ingition sense has a

12v feed but didn't start the engine , the voltage on both switched and permanent 12v lines dropped to just 5v. When I started the engine the voltage went back up to 12v and everything started working. I've fitted a fair few stereos in the past and never seen anything like this before - I can't understand why the voltage should drop that much.

I didn't have time to finish off so once again I disconnected everything and I've just come back to look at it today. I've reconnected to the fusebox and checked that I have the correct voltages where the cable plugs into the car kit - all good. This is wired exactly as it was last time , but now it won't power up at all with the engine running or not. Thinking I may be going mad I've connected the permanent and switched 12v wires directly to the 12v feed going into the back of the fusebox - nothing. I definitely have the power going into it but there's no life.

That would suggest that the car kit is faulty , but just wanting to confirm things I popped the bonnet and connected it directly to the battery and it works just fine. Back to the fusebox - no life , back to the battery direct - working.

Now this is a total mystery to me. It seems to vary from week to week the situations in which it will and won't power up and I'm checking all the connections with a multimeter and it *is* getting power. Why should it be happy with 12v in one place and not in another?

Reply to
Dr Zoidberg
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It's that dodgy Czech build quality.

Should have bought a proper VW rather than a cheap Commie copy ;-)

Reply to
SteveH

Has it got a decent earth?

Reply to
Ged

Yes.

Reply to
Dr Zoidberg

What year is the vehicle? If its a newer model it might have CAN/VAN/ Multiplex wiring. Some ignition feeds will drop out and do funny things under very little current draw.

Reply to
Ged

It's an 06 octavia and it does have CAN-Bus wiring

Reply to
Dr Zoidberg

Are you using the ignition feed at the head unit? If you are I would probably try running a feed from the barrel or lighter socket (if its

12v ign), pick a nice think wire. The ones at the head unit and other locations are probably linked into the CAN bus stuff. I don't really understand CAN bus but I know it does some funky stuff when you try tapping anything onto it, any current draw can cause problems.
Reply to
Ged

....not sure what a think wire is...probably best to try a thick wire:)

Reply to
Ged

Nope , into the fuse box onto a couple of spare terminals

Reply to
Dr Zoidberg

Hmmm, I would try going onto the back of the barrel or lighter.....it would rule out any problems on the ignition at least.

Reply to
Ged

With it being CAN Bus, the fuse box most likely isn't just a fuse box. It'll have a CAN controller built in, and chances are you've probably picked up two fuses that are controlled by the CAN controller for optional extras. Hence the strange goings on with voltages.

Professional installers will always take a feed direct from the battery, and unless they can find a suitable ignition controlled wire, they'll wire the kit up so it's permanently on. It just means you don't get the option of the phone turning off with the ignition (most handsfree kits will work with the igntion off anyway).

Reply to
moray

The fuse that I've used for the switched live is labelled with a phone symbol , suggesting it's designed for a car kit. The other one I can't remember off the top of my head.

Indeed.

I'd rather not have the continual drain , even if it is low. Looks like I'll have to try and find a route through from the engine bay for a permanent 12v though

Reply to
Dr Zoidberg

I would personally take the feeds from the back of the barrel. Good luck with it whichever route you go.

Reply to
Ged

Trying to wind us up again Steve ;-)

Reply to
Chris Bartram

I need new bait, Zoidberg appears to be immune to the stuff I'm using ;-)

Reply to
SteveH

It's fairly old and stinky , and normally Zoidy will eat anything!

Reply to
Dr Zoidberg

The carkit will power itself down if there's no phone connected, so I wouldn't worry about it.

Reply to
moray

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