My Landie has been eating alternators, six over the last 4 years.
Although I am guilty of bolting on some dodgy old items I am sure this
is a fault in the wiring which is getting worse. My battery is low
this morning so it hasn't been charging even though the warning light
has not been on. Previously I all but ran out of electrics one night,
then just as I was about to break down suddenly the alternator started
working again. I replaced that alternator (brushes were OK, I had
replaced the regulator some weeks before), checked everything and it
all seemed fine, now it has stopped charging again. Previous
alternators seem to have overheated, and a couple have failed with the
charging light coming on when I turn the ignition off (a bad sign, and
I haven't been welding it).
I am wondering if there is an intermittent break in the warning light
circuit to the alternator. I think there is a resistor in there
somewhere, but I don't know what it looks like (or is it resistance
wire in the loom?). Anyone have any ideas ? I have been thinking of
running a separate control wire to the alternator outside the loom,
but need to figure out what to connect it to at the dash end. Anyone
know how this bit of circuit works ?
First I would carefully check the battery main leads, especially the live to
the starter and also the alternator connection to this point. Also make sure
there is no short to ground as well with damaged insulation on these leads.
Check condition of live connection at alternator itself.
The warning light wire to the alternator is an ignition live fed through
the resistance of the bulb.
Anyone have any ideas ? I have been thinking of
The warning lamp is fed live from the ignition switch on one side, and
earths through the alternator on the other when engine is stationary but
when the alternator starts to charge with engine running this alternator to
warning lamp earth connection goes live and extinguishes the bulb as it
won't work fed with a live at the same potential on both terminals.
Sometimes a slightly glowing warning lamp with engine running indicates
there is still a potential (voltage)difference due to a faulty connection or
ignition feed so check everything from ignition switch to alternator.
Warning lamp lit with ignition off and engine stopped is usually a fault in
the alternator (diode feedback etc.) Note, without warning lamp lit
initially the alternator (but not all types) will not start to charge.
I would start by running a new wire to the warning light. So that you
know there is nowt dodgy going on with it, and know what is connected to
You just need to put 12v to one side of the bulb and connect the other
side to the alt. There is nothing else in the circuit.
On 1 Apr, 14:22, Austin Shackles <austinDITCHTHISFORBETTERRESU...@ddol-
Thanks to all responders. I assume that the separate resistor I see on
some wiring diagrams must relate to the older external regulators for
alternators, so I have got the message. Live to charging light to
I have just done a quick check. Alternator earth to chassis is
perfect, no resistance. Warning light bulb still lights, so bulb is
I gave the battery a short charge this morning so I get the following
With ignition off - 0V to the control wire, 12.2 to the charging
With ignition on, engine not running - 1.5V to the control wire, 12 to
the charging terminal, ignition warning light on
With engine ticking over - 12.7V to the control wire, 12.5 on the
charging terminal (how can this be lower ??), ignition warning light
The last one has me foxed. I measured the battery voltage and no sign
of charge getting through when I blip the throttle, still 12.5V.
The control wire on the alternator reads 12.5ohms resistance to ground
with everything turned off, so I suppose this is how the current flows
through the ignition warning light when the ignition is on.
I am wondering if I have an intermittent short or break somewhere
which is causing arcing or something that tends to mess with the
alternators. If the output lead from the alternator was making and
breaking, e.g. at the starter solenoid connection would it cause
voltage spikes and mess things up - I suppose there is an inductive
load there ?
I think I may rig a full circuit direct from the battery both ways to
check the alternator, eliminate any possibility of wiring shorts. If
that doesn't work then it has eaten another one - and it was OK when I
fitted it 2 weeks ago, and has barely done 50 miles since. I am loathe
to fork out for a good new one until I can figure out why it has eaten
so many. One of them completely overheated while I was driving, filled
the Landie with the smell of hot electrics, and I had only driven 5
miles, in the winter.
Its the IGNITION LIGHT RESISTOR that has got me confused - I suppose I
can check its presence by removing the charging bulb and check if
there is a resistance between white and the alternator field ?
See this thread http://forums.lr4x4.com/index.php?showtopic 385&hl
Look on the wiring diagram just below the battery, it says IGNITION
LIGHT RESISTOR. This appears on all my Land Rover wiring diagrams
(which are genuine Land Rover and not Haynes upside down misleading
Looking at that, it's a by-pass of the ignition warning lamp between the W
(white) ignition feed for all the warning lamps and the warning lamp 'd' NY
( brown/yellow) wire connection to the alternator. It's probably about the
same resistance as the warning lamp bulb and is probably added to ensure
initial start up of the alternator even if the warning lamp blows so you're
not stuck without charging in some remote area. I can't see it being
necessary but can be another feedback path in the case of faulty alternator
diodes but it's no different than having the bulb in circuit. Strange
things, these Land Rovers.
Good thought Martin. It had me mystified, but what you suggest not
only makes sense it explains why it doesn't matter in 99.9% of cases
if it is not there at all. With that in mind I am much happier
bypassing the entire loom and trying a direct battery to alternator
and back loom-bypass operation.
I'm not sure exactly what you mean by that but don't forget to put a small
wattage bulb in the circuit if it's the warning lamp wire you are talking
about, that would be OK. If it's the output wire (heavy) you are talking
about, that goes directly to the battery + , although sometimes in a
On or around Wed, 2 Apr 2008 22:29:21 +0100, "Oily"
normally either goes to the starter terminal or direct to the battery.
Worth checking it, although they rarely give trouble. Losing the output
connection can lead to over-voltage in the alternator and frying of
regulator or rectifier diodes.
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
About that Charging Light Resistor.
I have disconnected the field wire at both dash and alternator ends
and there is a resistor in there of about 82ohms connecting the field
wire to the white (switched live). Which I reckon is equivalent to a
1.5 watt bulb. Heaven knows where it is (I still think it might be
resistance wire in the loom), however Oily suggested it would be about
the same as a bulb to keep the charging going should the bulb fail. I
wonder if it is a dummy bulb because the small circuit board idiot
lights fitted on the 90/110 don't really work on their own with a
Anyway - the things exists - but all checks on that side seem OK.
Can't find a short or a break.
I am beginning to suspect the output wire from the alternator to the
starter solenoid, so will attack that next - though its a bit tucked
away behind the manifold on the V8.
If I can find the problem then a nice new alternator might be in
order, but not until !
Definitely check the output wire to the battery +, usually connected direct
to the main supply lead on the starter, unless someone has fitted an ammeter
with a dodgy connection, I've seen this a few times. If this is disconnected
it's normal to have a fried alternator. Problems with the warning lamp
normally only result in no alternator output, but no damage. I didn't know
it was a V8, the starter leads are in a vulnerable position here and could
easily have a short or burnt connection.
Think I have found the fault. I ran a new output lead all the way from
the battery to be certain, and with the old lead still in the loom I
ended up with two fat leads at the alternator. So I thought best
connect both, at least for testing. That meant both had rubber
protection boots so cut the boot off the old lead, and there was a
nasty crimped and corroded mess. I reckon that was the source of the
problem, and hidden by the rubber boot it has killed a succession of
One of my old tired alternators is still working (which amazed me) so
have that in place till I find a nice one to go on. I think the
standard one for the 110 V8 is an A127/65 with pillar type
connections. However there are all sorts of variations out there, some
with plug type connectors, right hand and left hand.
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