Technical ignition light on under revs

[sprie]

I can't work out what will be causing this.

I turn the key (ignition light on), wait for glow plugs, start engine (starts immediately) and ignition light goes off.
If i then rev the engine, ignition light comes on - there is a bit of flicker as the revs goes on and off but basically it stays on under revs, goes off when low/idling.

I had a look at the connection to the alternator and that looked fine. I removed the connections to the battery, gave them a clean, and put them back on.
The battery was very low (but not so low that it wouldn't start the engine), so i put my battery repair/charger on it and after a day or so, it was back to full.

The battery and the alternator are new this year.

I don't understand enough about the charging circuit to understand what could be causing the light to come on.

fiat 1.9 turbo diesel

 

[bugsymike]

I can't work out what will be causing this.

I turn the key (ignition light on), wait for glow plugs, start engine (starts immediately) and ignition light goes off.
If i then rev the engine, ignition light comes on - there is a bit of flicker as the revs goes on and off but basically it stays on under revs, goes off when low/idling.

I had a look at the connection to the alternator and that looked fine. I removed the connections to the battery, gave them a clean, and put them back on.
The battery was very low (but not so low that it wouldn't start the engine), so i put my battery repair/charger on it and after a day or so, it was back to full.

The battery and the alternator are new this year.

I don't understand enough about the charging circuit to understand what could be causing the light to come on.

fiat 1.9 turbo diesel

Normally I would have said alternator brushes worn out, but you say new alternator.???
Have you put a voltmeter across battery terminals, usually if all good when you bring the revs up even with headlights on it should show around 14.volts as a guide.
Is alternator under warranty?
I trust nothing silly like slipping drive belt?

 

[Communicator]

I am thinking that an increase in voltage, and hence charge current when engine is revved causes a voltage drop at a high resistance connection in the charging current path. Check and clean connections at main chassis earth point, just forward of RHS engine mounting. Do same with engine block earth at starter/clutch housing.

The "ignition" or alternator warning light is connected between the ignition switch and the alternator field circuit at the D+ terminal.
With engine stationary and ignition on, the D+ is at 0V. Current flows from the battery through the warning light, to the alternator field. This gives the initial excitation supply to the alternator. With the engine running and alternator generating, the voltage at the D+ terminal will be equal to battery voltage. There is then no significant voltage across the warning light, so it goes out.

The circuit may be traced on the attached diagram.

 

[sprie]

Normally I would have said alternator brushes worn out, but you say new alternator.???
Have you put a voltmeter across battery terminals, usually if all good when you bring the revs up even with headlights on it should show around 14.volts as a guide.
Is alternator under warranty?
I trust nothing silly like slipping drive belt?

It was a new alternator, about 3 months/100 miles ago.
I have double checked: the belt is good and not slipping.

I tackled the earth strap from the gearbox to the body. It looked fine, but i removed both ends, cleaned both the gearbox/body fixings and the strap itself (which is the original webbed strap) and refitted. On testing, i got the same symptom.

The earth strap from the battery to the body i had replaced previously. I can't remember why - it might have been looking tired or maybe the battery was slightly larger and needed a longer strap. Anyway, i hadn't replaced it with the web strap - i have used a sheathed wire strap. I have checked my order, and it says it is good for 110 amps. This is what i bought:

https://www.amazon.co.uk/dp/B07DPV2CRW?ref_=ppx_hzod_title_dt_b_fed_asin_title_0_0&th=1

and this is it in place on the ducato

PXL_20251110_102650619.jpg

www.amazon.co.uk

 

[jackwhoo]

New parts can be poor and fail early.....you dont say what brand new alternator is?

 

[Eternal Optimist]

It may be worth temporarily mounting a jump cable from the battery negative to the engine block simply to rule out any earth continuity problems. If the ignition light comes on with this arrangement the problem isn't the earth path.

 

[sprie]

It may be worth temporarily mounting a jump cable from the battery negative to the engine block simply to rule out any earth continuity problems. If the ignition light comes on with this arrangement the problem isn't the earth path.

that was a good idea. Just tested it out (twice) using jump leads from the negative on the battery to a couple of earth points - unfortunately, symptom still annoyingpresent.

New parts can be poor and fail early.....you dont say what brand new alternator is?

I bought it from coastal motorhomes - it is AS brand (looking at the box in the photo)

Fits Fiat Ducato Alternator 1.9D+TD 1930cc 75amp (1994-2002) 1305709080

New Alternator 75Amp Fits Fiat Ducato1.9D+TD 1930cc (1994-2002) SpecificationsVoltage: 12VAmp: 75ASize A: 42mmSize B: 16.5mmSize C: 82.5mmG qty: 5O.D.1: 62.5mmPulley APD.1: 10.5mmD.2: 12.5mmD.3: 12.5mmL.1: 190mmPlug: PL_9104 Please Be Aware There Can Be More Than One Option Fitted To These...

coastalmotorhomes.co.uk

 

[jackwhoo]

Battery voltage engine running at idle?
Battery voltage engine running at higher revs and battery light on?
Battery voltage engine running at higher revs , battery light on , headlamps on?

 

[jackwhoo]

If you can. Safely disconnect the d+ , run a wire from d+ to an inline 1.2w bulb and on to battery +
See if the inline bulb behaves in same way as dash charge light.

 

[Communicator]

What has not been mentioned previously in this discussion, is the power distribution point designated BB10 in the wiring diagram. It is shown at the LHS of the diagram that I attached to post #3. On my 1990 Talbot Express this connection was a 4 way 9.5mm male blade connector mounted on the RHS inner wing and was partly obscured by the blue glow plug relay. See attached photo. The BB10 shown in the x230 wiring diagram will probably be similar. On a basic vehicle all 12V power, other then starter motor current, is routed through this connector. It is therefore just as important as the various earth connections. If the connections here are even slightly high in resistance, the heating effect could gradually make matters worse. I suggest that this connection point is carefully examined, but with the battery negative disconnected for safety.

 

[sprie]

Battery voltage engine running at idle?
Battery voltage engine running at higher revs and battery light on?
Battery voltage engine running at higher revs , battery light on , headlamps on?

sorry for delay in responding.
Voltages:
no engine running: 12.82.
engine idle: 15
engine high revs (ignition light on): drops down to 13.5
engine high revs (ignition light on), turn on headlights, drops down about 0.3 to 13.2

 

[sprie]

What has not been mentioned previously in this discussion, is the power distribution point designated BB10 in the wiring diagram. It is shown at the LHS of the diagram that I attached to post #3. On my 1990 Talbot Express this connection was a 4 way 9.5mm male blade connector mounted on the RHS inner wing and was partly obscured by the blue glow plug relay. See attached photo. The BB10 shown in the x230 wiring diagram will probably be similar. On a basic vehicle all 12V power, other then starter motor current, is routed through this connector. It is therefore just as important as the various earth connections. If the connections here are even slightly high in resistance, the heating effect could gradually make matters worse. I suggest that this connection point is carefully examined, but with the battery negative disconnected for safety.

I can see this on my van, it is behind the battery. I will need to remove the battery to get enough access to it to be able to remove/clean up connections - I will do this when i get a moment.

 

[sprie]

If you can. Safely disconnect the d+ , run a wire from d+ to an inline 1.2w bulb and on to battery +
See if the inline bulb behaves in same way as dash charge light.

I will investigate

 

[jackwhoo]

I think you may well have a bad diode in the alternator.
Your symptoms were common on fords in the late 80s early 90s. when ford with a very flat battery was jump started then left running on the vehicle alternator it was too much for the alternator and damaged a diode.

 

[jackwhoo]

How to Test Alternator Ripple Voltage with a Multimeter | Fluke

A step-by-step guide with key terms, and best practices for testing alternator ripple voltage with a multimeter.

www.fluke.com

 

[Communicator]

I think you may well have a bad diode in the alternator.
Your symptoms were common on fords in the late 80s early 90s. when ford with a very flat battery was jump started then left running on the vehicle alternator it was too much for the alternator and damaged a diode.

I am finding this post interesting, but I am struggling to understand how even 500mV of ripple would cause a 12V 2.2W bulb to emit light? I think that there would have to be rather more than 500mV, perhaps caused by an undetected relatively high resistance in the charging circuit? A ripple test across the battery may not give the whole picture, as the common point between alternator, battery, and ignition switch connection for the warning light, is the BB10 connector. As a ripple test is easy to perform, then checking at the battery, and if a fault is suspected at BB10, to battery negative if practicable may reveal something.

 

[sprie]

1 step forward, 3 steps back today.

I had a go at the ripple test, measuring on the battery posts (the connections at the alternator were a nightmare when i installed the alternator, as there is a plastic shroud around the connectors, which provides protection but makes it hard to tighten up the nuts, but the cables at the alternator do seem firmly in place):
- at idle with headlights, fog lights and fan on, my multimeter should 0.07 AC volts
- under revs (with the ignition light on), the multimeter had the same 0.07 AC volts
- but then when i dropped back to idle, the ignition light now stays on

i.e. i have ignition light on all the time.
I then measured DC volts again:
- battery is about 12.6v
- running engine, it measures 12.2v

Does this mean either the alternator is completely duff or there is broken connection from the alternator back to the battery?

(i have tried putting a jump lead on, from the body of the alternator back to the negative on the battery but that made no difference)

 

[Mike1alike]

engine idle: 15

the multimeter had the same 0.07 AC volts

A shortcut on the battery can get a diode toasted. Touching the jump cables between them while connected on the battery does that.
AC voltage that comes out of the alternator should be under 50 mili Volts.

If even one diode fails two things will happen.

• The DC field will be out of balance with one side of the bridge producing more current than the other. This can be heard and felt as a low pitch vibration originating from the alternator (different than a bearing noise).

• The out of balance field on one side of the rectifier bridge will begin to overload the remaining diodes on that bridge. This overload will cause a DC voltage increase on the failing side as the remaining diodes overheat and begin to allow AC voltage to bleed through. An oscilloscope can verify this condition.

Somehow your voltage regulator cuts the charging too at some point, when you have 12.2 V with the engine running.

 

[Communicator]

1 step forward, 3 steps back today.

I had a go at the ripple test, measuring on the battery posts (the connections at the alternator were a nightmare when i installed the alternator, as there is a plastic shroud around the connectors, which provides protection but makes it hard to tighten up the nuts, but the cables at the alternator do seem firmly in place):
- at idle with headlights, fog lights and fan on, my multimeter should 0.07 AC volts
- under revs (with the ignition light on), the multimeter had the same 0.07 AC volts
- but then when i dropped back to idle, the ignition light now stays on

i.e. i have ignition light on all the time.
I then measured DC volts again:
- battery is about 12.6v
- running engine, it measures 12.2v

Does this mean either the alternator is completely duff or there is broken connection from the alternator back to the battery?

(i have tried putting a jump lead on, from the body of the alternator back to the negative on the battery but that made no difference)

Yes, unfortunately it does suggest something like. Are you able to check your multimeter an another vehicle/battery?

 

[Communicator]

1 step forward, 3 steps back today.

I had a go at the ripple test, measuring on the battery posts (the connections at the alternator were a nightmare when i installed the alternator, as there is a plastic shroud around the connectors, which provides protection but makes it hard to tighten up the nuts, but the cables at the alternator do seem firmly in place):
- at idle with headlights, fog lights and fan on, my multimeter should 0.07 AC volts
- under revs (with the ignition light on), the multimeter had the same 0.07 AC volts
- but then when i dropped back to idle, the ignition light now stays on

i.e. i have ignition light on all the time.
I then measured DC volts again:
- battery is about 12.6v
- running engine, it measures 12.2v

Does this mean either the alternator is completely duff or there is broken connection from the alternator back to the battery?

(i have tried putting a jump lead on, from the body of the alternator back to the negative on the battery but that made no difference)

Sorry, I missed that part. I find 1/4" drive sockets useful. You would probably need 8mm, and 10mm sockets, but 7mm fits jubilee style hose clips.