Hi, 

I need some advice.. i have mk2 focus and i tried to change the stock radio for a sony single din head unit. IT WONT WORK?!?!?! i took it to halfords where they tried the unit which worked, then they tried testing the cables in the car which were showing as having power, yet when attached there's no power to the unit.. I'm getting frustrated with it now..

Any advise would be amazing!

Have you tried swapping the battery and ignition live wires at the original quadlock connector?

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Sent from my SM-G930F using Tapatalk

I haven't changed them over but I did change the connectors on the wires them selves the red to the yellow and yellow to the red but still nothing coming on.. 

If there is power to the cables in the car, and the radio works out of the car, then you need to do some troubleshooting. Is there a decent ground at the radio end of the harness?

I honestly wouldn't know how to check... in the past I just put radios into cars an they have worked without having to mess about, Halfords done the testing for me and then told me to call back next weekend to see their fitting expert... as the two guys dealing with it were just as stumped as I was :)

You should always have power on the permanent connection, and only power on ignition with the other. The Ground pin is the one next to the ignition sense pin, with the empty space above it.

You can do this with a multimeter if you have one on 20V DC range, if not, £5 on ebay will get you one suitable for car electrics only (do not try using on mains, they like to explode if any fault occurs). You should have 11-14v between the pins. It's a worthwhile investment.

If you haven't got a multimeter you may be able to use a W5W bulb (draws approx 500mA), between both pins and ground. It should light if voltage is there - this may have a better show of if the ground is actually good vs just making a tiny bit of connection.