electrical problem with 2002 ford focus

I need help and I hope someone out there can help:
Last week I bought a Late 2002 Focus ( Newer Shape ). However after driving it for a week I have discovered that after driving for a bit
(20 mins or more) The needle on the speedo will suddenly "sweep" up the dial, the volume on the stereo goes up and then it all goes back to normal. sometimes this happens more than once and sometimes it doesn't happen at all. However it is becoming more regular. I talked to the riginal owner and he said he had been back and forth to the local ford dealership and they kept telling him there was nothing wrong with the car. I have noticed today that after the car has this power surge thing you can see, if you look really closely, that the lights on the dash and the main lights pulse very slightly after this power surge thing.
I have read alot about the speed senser being the cause of a fault very similar to this one however the fault that needs the speed senser seems to be the reverse of my fault. they have a lose of power and I seem to be getting to much !
I would love some help
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ross snipped-for-privacy@ntlworld.com wrote:

Different symptoms, but probably the same cause. If it was my focus I would check / remake the earth, and if this didnt solve it I would swap out the speed sensor. Not a fun job I am told - had mine done under warranty ;)
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Richard Parkin wrote:

Very unlikely to be the VSS; if so, it's no big deal. 25UKP and 20 minutes under the car or 100UKP to a dealer.
Chris
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Chris Whelan wrote:

They arent the common symptoms of a VSS fault, but given the VSS is used to generate the control level for the Automatic Volume Control as well as for the speedo I would still be prepared to put 5 quid on it ;)
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Richard Parkin wrote:

I would have agreed with you had the OP not said that after the error occurs, the dash lights and main lights (whatever that means) pulse.
The VSS problem is mainly related to earlier cars. The fault with the sensor is that the connection between the pins of the connector, and the internals of the sensor fail. Later ones are improved.
It has also been to a dealer, where one would hope they would have changed the VSS by now if it was suspect. If that hasn't been done it would be worth the OP changing it if only as part of the process of elimination, but my 5 quid is on an earth fault ;-)
Chris
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On Sun, 25 Mar 2007 08:27:57 +0000, Chris Whelan wrote:

Great - all we need is for Ross to spend a hundred quid or so swapping the VSS to settle the bet ;)
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Yeah - mine did it on the standard headlights... not so much on the discharge ones.

See, that's where I cheated a bit because I had heard of them doing it ;)

Stick it in an NSPCC box next time you see one ;)
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