If a drain of that magnitude drops to zero when the alternator is unplugged,
which it should do, the alternator is at fault. But make sure your scales
are correct as most alternators *do* exhibit a very small drain in the order
of a few microamps and this is the normal reverse leakage of the diodes. I
suppose a diode could go leaky to the extent of 16mA, but normally when they
go they go full short which is pretty catastrophic for the loom. Because
the nine diodes are interconnected they interact with each other and so it
is not always possible to identify the faulty one without disconnecting one
end from the stack (which isn't recommended!). With the diode stack out of
the alternator (is it the type with the open heat sink vanes and the nine
individually identifiable diodes bonded to them?) You can check the reverse
characteristics of the three connected to the output terminal(s), the three
connected to the indicator terminal, and the three connected to the ground
terminal. If any of these exhibit reverse leakage greater than a few
microamps then the diode stack has to be replaced. If all those are OK then
the problem lies elsewhere. There are other electronic circuits inside such
as the voltage regulator which could fail with various leakage results, and
also conductive debris could have built up giving a partial short. But you
do not know whether you are seeing cause or effect and so just changing one
part that was effect of the real problem may only cause it to fail again, so
probably you would be best off swapping it for a guaranteed unit. In all
the alternators I have seen (early 70s on, 3 pin) the thin brown is
connected to exactly the same place at both ends as the thick main charging
brown, even though it goes to a different large spade as the main output
wire internally they are connected together. Maybe in the very earliest
internally regulated 5-pin alternators it was used as the 'sense' wire for
the voltage regulator to take account of volt-drops in the main charging
wire, but I haven't examined one of those.
PaulH.
----- Original Message -----
From: "Hans Duinhoven" <h.duinhoven@planet.nl>
To: "Paul Hunt (T)" <paul.hunt1@blueyonder.co.uk>; <mgs@autox.team.net>
Sent: Wednesday, December 31, 2003 3:43 PM
Subject: 16 miliamps drain - a verification
> 1 RESULTS OF TROUBLESHOOTING
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