Warning light on

[lumphammer]

This weekend I have just noticed that my ignition warning light is glowing, even though the ignition is switched off and the engine battery is switched off.

I have a Sterling alternator to battery charger and a 20A mains charger. The engine and domestic batteries are not connected, except through the earth.

Initially I found that if I switched off the battery charger and left the domestic batteries on, the light would go out, but by the end of the weekend it didn't make any difference what was on. I could isolate all the batteries and just run off the battery charger, or switch off battery charger and run off batteries the ignition light still stays on.

As I understand it, with the engine off, one side of the warning light is effectively grounded through the alternator. With the engine battery isolated the only way 12v can get to the lamp would be through the A- to - B charger.

Any suggestions or thoughts on fault diagnosis gratefully received

 

[Barry Jones]

I think you have a wiring fault somewhere.

You don't say whether this fault has existed since the Sterling A-B-C was fitted and has gradually got worse or whether it suddenly appeared one day.

By the nature of the fault creep, it sounds like a short somewhere and would need further investigation. Check all the connections first and look for water ingress/damp, worn insulation etc.

 

[pampas]

with the fault on disconnect the warning lamp at the alt. Should go out, if not then the fault lies from the lamp to the alterator. If this proves to be ok

then the fault is in the alternator and is probably one of the Trio diodes at fault. Not knowing the alt type, of Lucas type very simple to renew without a lot of stripping down. suggest a visit with Alt. to your nearest auto electrician for repair.

 

[oldsaltoz]

+ 1 for the above.

 

[Billjratt]

We still don't know the alternator/engine type.
If the alternator is modern, with internal regulator, the lamp is grounded through the field winding and regulator. The positive feed is from the ignition switch and on a simple diesel engine, that is all there is. (so the switch must be shorting) If there's more connected, then there are more opportunities. You mention Sterling -in this case you have a red wire on the battery and a yellow wire on the ignition switch - they could be the problem. If it's a petrol or common-rail diesel, there will be blackbox management systems connected.
If it's old and has a lucas alternator with relays outside and a mechanical regulator, they will need to be checked.
Got a meter? Switch ign off, black lead to alt - (may be isolated or chassis) + lead to :
term 61 (thin brn wire to ign lamp) should be 0v, will have a voltage in error condition.
Terminal 1 of ign lamp, "
terminal 2 of ign lamp, "
dead side of ign sw "
live side of ign sw - this is the first time you would expect to see battery voltage.
The highest voltage is where the problem lies.
You probably need to pull other wires off temporarily while measuring to determine where the voltage is coming from.

You don't mention whether there are any other symptoms - ie does it charge?
does the sterling cycle through it's programme OK?
Any other instruments/lamps (oil pressure, exhaust temp etc.) acting strangely?

DFT define the problem

 

[pampas]

"If the alternator is modern, with internal regulator, the lamp is grounded through the field winding and regulator"

Via three diodes Trio) which allow power into the machine, as the alternator internal voltage rises so the current in the warning light reduces until the warning light goes out,