how do i??

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how do i??

Postby armyphil » 12 Mar 2009, 17:24

trace a positive earth fault?? The battery keeps draining i know it s a good battery and the alternator is kicking out the right voltage but in a matter of hours the van is dead again!!! :evil:

Any ideas of how to do it or where the possible cause might be would be very muich appriciated

cheers in a advnce phil
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Re: how do i??

Postby jamesc76 » 12 Mar 2009, 18:09

Disconnect battery earth lead and attach test light in its place light will be lit up, then pull fuses till light goes out thats the circuit with the fault
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Re: how do i??

Postby armyphil » 12 Mar 2009, 20:21

you seem clued up james on electrics any reason why iam getting power to the ignition warning led on both sides of it but it doesnt come on i have a blue wire under the dash and one from the alternator going straight to the batt pos?? it still doesnt come on though any ideas??
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Re: how do i??

Postby AngeloEvs » 12 Mar 2009, 21:06

You should only have a voltage on both sides of the LED once the alternator kicks in. With just the ignition on only one side of the LED will 'have 12V and the other side effectively 'grounds' via tha Alternator and the LED lights.
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Re: how do i??

Postby jamesc76 » 12 Mar 2009, 22:13

As above if you think of it this way the battery gives say 12.4v to bulb when just ign on not running so its earths via the alt. when running it gets say 13.5v from alt so the power over comes the 12.4 from the battery and makes it go out !
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Re: how do i??

Postby armyphil » 13 Mar 2009, 16:06

so i need to find the earth point for the LED??

how come i have [power to both sides? its a mystery
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Re: how do i??

Postby AngeloEvs » 13 Mar 2009, 19:00

The alternator provides the earth point when it isn't generating voltage. One side of the LED is supplied from your 12V ignition and the other side, whilst the Alternator is stationary, it connects to ground via a connection on the Alternator (this is done by the alternator and I won't go into the technical details). As James says in his post, once the alternator starts spinning, this same connection instead of being an earth path produces 12V and the LED goes out since it no longer has an earth path. If you get a bullb and connect both ends to a 12 V supply it won't light. You should have a blue wire from the Speedo Pod multi connector, this connects the ignition LED to the Alternator so check the blue wire on the Alternator is connected and in good order. With the ignition on and the engine off, measure the voltage at the blue wire on the Alternator - it should read 0V. If it reads 12V then you may have:

a) a duff connection on the alternator

b) a duff Alternator

c) a short circuit LED but unlikely.

d) incorrect wiring or a short circuit from elswhere.
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Re: how do i??

Postby armyphil » 14 Mar 2009, 16:18

thanks for that i will get onto it.

take it, it is an MOT failure if it doesnt work??
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Re: how do i??

Postby jamesc76 » 14 Mar 2009, 16:34

wether or not the alternator is working is nowt to do with the MoT but a warning light lit might be !!! By the sounds of it your alt. is fubared
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