I tried to fit a new stereo with 2 extra earth wires, Unfortunately they touched the chassis and sparked, The car wouldn't turn over and had to goto dealer, they reported "NO LIVE TO PCM RELAY" and they got it working, They wouldn't tell me how they fixed it(surprise) Can anyone shed some light on this, Many thanks in advance.
subject line de-mystified
Edited by Pugugly on 30/03/2008 at 12:13
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No year and engine; but earth wires don't spark....
Sounds like you'd blown a fuse to the immobilizer.
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No year and engine; but earth wires don't spark....
A common misconception. Current flows through the earth conductors so they can spark.
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OK; let me put it in simplistic terms.
If a vehicle cable connected to a battery neagive - an "earth wire" - chafes to the "chassis" it doesn't spark.
If it sparked; it therefore wasn't an earth wire - it was a live wire.
Everyone got that now....?
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OK; let me put it in simplistic terms.
snipquote
Sorry, I was being pedantic (I teach electronics at a university). The OP referred to the two earthing conductors on his stereo touching to chassis.
In fact in many systems (including cars) you can get appreciable voltages developing at different points in the earthing circuit due to high currents flowing (resistances at cable junctions and rectifying properties of interfaces between different metals).
Edited by Dynamic Dave on 30/03/2008 at 19:59
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Look like you mistook the orange/black live feed to the radio for an earth and blew the Radio fuse, F72 and the Main power fuse, F7 which are in the same circuit. They would simply have replaced/reset those 2 fuses, half an hours labour minimum charge (£35-£40 ?).
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blew the Radio fuse F72 and the Main power fuse F7 which are in the same circuit.
I'm curious, is there no discimination?
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Hi guys Cheers for response.
Earth wires can spark if there is power to the units which i think there was, All fuses were ok, I was told that the pcm relay is under the airfilter. I am just wondering if there is an inline fuse that they won;t tell us about.
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Hi Me again, My car is a Mk3 mondeo 2.0 TDCI zetec s
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Hi Guys. When I fitted the stereo it worked even after the earths sparked(it was anly a tiny spark), but when I come to start the car it wouldn't turn over, The stereo still worked. I still think the problem was that I didn't disconnect the negative on the battery.
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>> blew the Radio fuse F72 and the Main power fuse F7 which are in the >> same circuit. I'm curious is there no discimination?
Yes the Main fuse, 50A, supplies the main fuse box and circuits that run off it. The Radio fuse, 20A, is one of the circuits that run off the main fuse box. Ergo a current >20A but 50A so could blow both fuses simultaneously.
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Hi, Thats the strange thing I didn't blow any fuses. I fitted the stereo and everything worked except the car wouldn't turn over.
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Dazzie
You must have blown at least one; or you wouldn't have had a problem. If you'd burned out a main feed, the garage would have said so.
To lose the feed to the ECU relay - and lose cranking; it suggest the immobilizer wasn't deactivating.
The garage would have had no interest in finding out what had happened; they would just have plugged it in and they likely got a code for no feed from the relay, the guided fault-finding list for that code said check fuse X, it was blown, they replaced the fuse, it then started - "Great - write the bill."
The car's now fixed; what's the problem?
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Hi, They said when they first tried the diagnostic it wouldn't connect, I took stereo out when It went to ford, so now I have to try again, This time I will disconnect battery first, Then connect earths then units then battery.
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IIRC the Main fuse doesnt look like a fuse, it looks more like a relay and visually it would be difficult to tell if it was blown (or tripped). The garage probably just replaced (or reset) it.
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I assume the radio was still working as you took a live feed from somewhere else because you had mistook the original live feed for an earth.
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I didn't mistake any live for an earth, i am not colour blind.Basically I sort of fitted the stereo in reverse, I wish I hadn't started this now, I tell you, The fuses are ok, then you say a fuse has blown, Then I tell you what I did with the earths which are black, then you say I must have connected a live to ground, I came on here for advice not to be Insulted, I do know what the colours are for, Like I said before the only mistake I made was NOT to disconnect the battery OK..
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Don't be nasty - have a pasty. It's difficult to pitch comments sometimes as assumptions are made, so please keep it civil !
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I'm sorry you took my posts the wrong way Dazzle, I assure you I was in no way implying that you were colour blind (whatever that has to do with it), nor was I intending to insult you, I was merely offering suggestions as to what might have happened. If your attitude to helpful suggestions is to take offence then so be it, I will keep my suggestions to myself as far as your questions are concerned in future. Not all black wires are earth BTW.
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