new alternator not working

had an isue with the alternator on my 300tdi defender after some serious wading, (so did 3 others in the group) if i hit it with a hammer it would work again and put the warning light out for a few minuets.
Now to be on the safe side i bought a new (denso) alternator, fitted with a new belt and all seemed fine for about 5 minuets, now the warning light is on again.
Ive checked all the conections again and again and even tried swaping terminals but all in vein.
It would appear as though the light is wired to the rev counter terminal as it gets brighter the higher the revs but does the same on both D+ and W terminals.
I have done many searches and cant seem to find a definative answer, the original alternator had 3 terminals as does this one, B+ D+ W and 4 wires going to it.
I now i should only require 2 wires, the loom does not apear to have had any additional added.
any help would be apprieciated cheers

Daft question, but is the alternator earthed?

B+ to batt
D+ to warning light
W for tacho, not required to make it work.

if you've wired it all up correctly, then look at your battery being knackered.

Take it somewhere for a free check, or stick your multi across it and see what it is producing with the engine off.

what are the colours of the 4 wires you got going to it?

Oldseadog said:

Daft question, but is the alternator earthed?

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I did consider that and have been tonight and tried it with a jump lead but still the same

trax said:

B+ to batt
D+ to warning light
W for tacho, not required to make it work.

if you've wired it all up correctly, then look at your battery being knackered.

Take it somewhere for a free check, or stick your multi across it and see what it is producing with the engine off.

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Ive got two very large batteries, less than 8 months old each, both identical, both have independant battery isolators and the light stays on with either battery isolated, the only way it will put the light out is by isolating both batteries.
It is wired as per above. ive even tried disconecting everything bar the battery + and putting a lamp between B+ and D+, that lamp remains lit when started, although it does excite the alternator.
With a voltmeter between - and b+ i recorded 12.23 V with out the engine not running and 13.99 with the engine running

nrgserv said:

what are the colours of the 4 wires you got going to it?

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The wires are as follows
B+ = Large brown & small brown
D+ = brown and yellow trace
W = White

With the engine running, what voltage do you get between D+ and earth?

oldseadog said:

with the engine running, what voltage do you get between d+ and earth?

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18 - 19 v

top-cat said:

With a voltmeter between - and b+ i recorded 12.23 V with out the engine not running and 13.99 with the engine running

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Oldseadog said:

With the engine running, what voltage do you get between D+ and earth?

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top-cat said:

18 - 19 v

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reckon the new alternator has a goosed regulator.

not quite high enough b+ to earth
too high d+ to earth

nrgserv said:

reckon the new alternator has a goosed regulator.

not quite high enough b+ to earth
too high d+ to earth

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its looking likely
Its giving the same problem as the old one that was my only concern, although when i took the old one off it was siezed

That is why your charge light is on!

What is happening is that the voltage on your D+ is high enough to give you the equivalent of the 12V + fed to the charge lamp being a lower voltage than the 18V from the D+ terminal.

Have your alternator checked, as it sounds as though you have a faulty regulator ... Sorry!

top-cat said:

its looking likely
Its giving the same problem as the old one that was my only concern, although when i took the old one off it was siezed

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I just spat kebab at the screen.........

thanks for the advice guys, bloody typical i turned a cheap alternative down at |£58 and went with a denso one at £130 to avoid any problems.
Trouble is im laning in wales this weekend and wont have time to get it swaped between now and then, so fingers crossed itll cope for the weekend