A couple of weeks ago I bought a Sony Ericssson car kit from VRSTu.

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 (fuse 7 for switched 12v and 17 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 but didn't start the engine , the voltage 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?

I've had it suggested that in cars with CAN-BUS wiring you can get unpredictable effects when you add electrical extras.

I might have to run a dedicated power feed from the battery.

Any suggestions on how to get a wire through from the engine bay?

I've had it suggested that in cars with CAN-BUS wiring you can get unpredictable effects when you add electrical extras.

It still wouldn't explain why it worked faultlessly in my car Alex. As I said in the PM have you extended the cables when you had it mounted behind the glovebox? I didn't think there would have been enough cable to get you right over there.

I've dug out this old picture which might give you some idea of how I had it installed.

Under the dash, behind the headlight switch there is the main aluminium cross bar. I had it stuck on there.

The yellow wire with the red tape was the perm live and the yellow the switched. You can also see I had it grounded on the top

screw of the fuse box. The other yellow (Mute) along with the L&R audio go along the back of the dashpod to the radio.

Was in the car from day one, best part of a year, without missing a beat.

When you have it connected to the fuse box, are you using the terminals that I crimped on for you, directly into the output side of a spare fuseway or are you using scotchlocks?

No cables have been extended (it does reach , just, but I've been doing testing with it on the floor of the drivers footwell) , the earth is onto a screw that goes through the same frame that the fusebox is mounted to , and the two live wires are clipped into the output side of the fusebox with new fuses in place.

Like I've said , I've checked the power at the connector where it goes into the control unit and it does seem to have 12v , it just won't play nicely :(

Just a thought but have you got the telemute connected on the right pin of the radio?

I did have , but when doing testing it's not connected to anything