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300tdi Alternator

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Hi all, Not posted for a while but I keep lingering about reading the odd topic :D

I've had a Discovery 300tdi fitted to my 90 for around 4 months now, when it came to connecting the Alternator "Charge Indicator" (Thats what it was called on the 2.5N/A according to the Haynes Manual) we just sort of guessed.

There are 3 Terminals on the back of the Alternator, 1 was clearly the main feed (bigger and had the right fitting already on it) and then the 2 others. When the cable from the 2.5N/A loom was connected to one the charge light came on without the Engine running (Ignition on state I thought?) - so it was secured and forgotten about. The other terminal produced no reaction from the Charge Light (Battery Symbol on the Dash).

Now more and more the Charge light comes on, usually flickering into life, when the Truck is at idle, sort of like when I slow down at a Traffic light or a junction. I then thought the Alternator was dead or dying, but the odd thing is if I put full headlights on the light stays OFF when the truck comes to idle, if I turn the lights off the Charge light comes on and then even stays on if I turn the headlights back on (this test was done on the drive, not wanting to confuse other road users :D).

It's been doing this for around 2-3 months now and the battery hasn't shown any symptoms of being flat or low, still cranks the engine over fine.

My initial thought was that I had connected this Charge Light warning to the Rev Counter feed (with it coming on at Idle), but if I swap the connection to the other Alternator terminal (the one thats spare, I have no Rev Counter, guessing the other Terminal is the RPM Sensor Feed?) the charge light stays off always, no matter if the Ignition is on or off.

I feel I may have to live with it for the rest of the trucks life, as trying to mate a 300tdi to a 2.5N/A wiring loom was 'fun' anyway, the fact it's still running after 4 months is a surprise to me.... :D.

Anyone have any idea? Working nights and I'm a bit bored (hence the HUGE post :D - can't say I didn't explain it well enough though ;)).

As a side note - not really worth starting a new topic for - I am using the old 2.5N/A Temp Gauge with the 300tdi sender and the reading always looks high, it always sits at just under 3/4 "hot" every so often creeping up to the lower red band then back again. The Truck looses no water and I haven't added any since I installed the engine and topped it up. Do I need a 300tdi Gauge to fit the sender, think I recall it being mentioned they need to be a matched pair?



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I am afraid that, from your symptoms, I can't work out a logical reason why, but the first thing I would check would be all of the earth straps and (in this case) especially the engine earth, and the battery connections too (all of them).

IIRC the charge-light circuit effectively supplies the alternator with a reference voltage which it has to beat. The fact that it is flickering means that the alternator is not beating it, and the only three things I can think of that would cause this are dodgy alternator, dodgy wiring or possibly that the alternator is not a match for the engine and has the wrong size pulley on it resulting in it turning too slowly. The most like of these is poor connections I think.

Hope this helps


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Thanks Rog,

Just thought I'd post a quick update. I had previously checked the Earth straps and battery connections I did so agian but this time removed them and brightened up the seating surfaces of each. Sadly made no difference (made me feel better though :)).

During all these investigations my Father noticed me under the truck and shed a little light on the "mystery", he was the main helper (read: He did most of it) when I fitted the 300tdi into the truck, and unknown to me he had "refurbed" the Alternator while I was at work as it had "white deposits internally" thought it looked new when I mounted it.

After speaking to the last owner of the engine, it was removed from the Discovery about 2 weeks before I bought it off him, only having limited weather shielding.

I'm guessing the Alternator is very very tired due to this weather exposure, so I think thats where 90% of the problem lies, still unsure about the non logical behaviour of the Ignition/Charge light however (off with full beam on yet on when engine at idle in daylight etc). Sadly my Dad is no auto electrician so only really cleaned up the outside and a very quick clean of the internal coil (from where he could reach)

Hopefully I think a new Alternator should solve things, and if not, I'll just have to live with it, as I said the Battery is showing no sign's of being low or discharged.



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