Ignition warning light always on

[kin74]

I spent last weekend in a trip with my 1969 GT6 Mk2, saturday afternoon I realized (in the sunlight it was not easy to spot) that the ignition warning light was always on. I though the alternator was gone and I expected the battery's dead in a short time. It didn't happen. I drove the car for the whole day, night and the day after to home and the battery was fine. The warning light was still on.

What should I look for?

[Velocita Rosso]

The warning light is a continuity to allow charging. I had a warning bulb blow so never noticed the bulb was not glowing and I was getting a flat battery if the thin wire from alternator to warning light is broken/damaged it will not glow or charge
You may have a problem with the thin wire from alternator
Just put a meter on the alt output and earth and it should show just over 14v charging whilst running, same across the
battery
When not running across the battery should just be 12v  Also after overnight, before starting just check that the alternator is not warm...this also shows that the diodes have gone and is discharging the battery  

[JohnD]

The light is ON all the time, and the battery is NOT going flat!
But I agree that a likely cause is the wire from the alternator to the ignition warning light.

When you turn on the ignition the lamp lights, because it is connected to the battery via the ignition switch and a current flows into the alternator.  
Once the engine is running, the potential from the alternator opposes that battery voltage so no current flows and the lamp goes out.

So if the alternator fails, there is no opposing current and the lamp stays lit.
If the alternator has not failed, as shown by the fully charged battery, then there is a  fault outside the alternator.  The wire cannot be connected to the alternator and must be earthed, so the current from the battery still flows.   So follow it from the lamp to the alternator, and find where.   It should be brown with a yellow trace.

But there are other causes.  If the wire cannot earth through the alternator, then it will stay lit.   This can happen if the engine earth has broken.     Triumph provided a lenght of wire mesh, that is often forgotten when removed for engine work, or else just rots away.     A length of stout starter cable - it has to carry the same current when starting! - will solve it for good.

A diagnostic sign of a poor engine earth can be found after a start up, especially if that does not happen 'on the button' and prolonged churning is needed.  A hot choke cable!    That is then the best way back to the chassis/body and battery for the current.

John

[WIMPUS]

I had this to, sometimes had no charge.
But discoverd the plug etc was very rusty and not giving good contact anymore.

I would let the car run and wiggle the plug and wires.
Could be that it goes out.

[Jonny-Jimbo]

Where is the engine earth cable on a Vitesse? Is it sump to chassis or round the engine mount?

[kin74]

Thanks all, I'll check wires and plugs.

[garyf]

Quoted from Jonny-Jimbo

Where is the engine earth cable on a Vitesse? Is it sump to chassis or round the engine mount?

The Vitesse Engine to Chassis earth runs from one of the Bolts on the Front Plate to the underside of the Chassis via a steering rack clamp bolt originally.

Make sure there is clean bright metal between the bolt/nut and the lug on the Earthing lead and coat in Waxoyl or grease after to stop corrosion.    

[stevegt6]

Some good points to check there.... I have similar related issues - Very dim ignition light and not starting 'on the button'

Will check the wires and earthing.

[JohnD]

There you go - no one (except Gary) knows where it should be!
Andit often isn't there.
But use starter cable and have an easy mind.
Mine goes from the block itself all the way to the battery earth point.

And Steve - a dim ignition light was my symptom of a lack of engine/alternator earth.
I attacked it with more and more powerful  alternators, with no effect (as you would expect)
I even called in a friendly electrical engineer, who was also baffled.
Until, as evening fell and it got a bit dark, he saw the corona discharge around the alternator, a blue glow, and the penny dropped.

John

[junkuser]

"saturday afternoon I realized (in the sunlight it was not easy to spot) that the ignition warning light was always on"
Was it just glowing or as bright as it shows when you turn the ignition on before starting the engine?

The lamp is between the battery voltage and the output voltage of the alternator so resistance difference in the in the wiring from each supply can cause the lamp to glow.  Very common, pretty much the rule rather than the exception.
Your description would fit the picture IF the lamp is only glowing.

[piman]

Hello Kin74,

does your battery area smell of sulphuric acid? That is the classic clue to overcharging which will also bring on the ignition warning lamp.

Alec

[kin74]

Update: yesterday I disconnected the alternator wires, cleaned and brushed the plugs, finally reconnected them. I started the engine and let it run in my garage for a couple of minutes and the light was off, I will test it better and longer next weekend.

[RobPearce]

Quoted from junkuser

The lamp is between the battery voltage and the output voltage of the alternator

Not quite. The "output" of the alternator is directly connected to the battery, so this configuration would short the lamp out.

The lamp is between ignition switched supply and the alternator's field winding supply, which is fed by the alternator independently of the main output. The field windings reinforce the magnetic field that generates the output (and this supply).

[WIMPUS]

Quoted from kin74

Update: yesterday I disconnected the alternator wires, cleaned and brushed the plugs, finally reconnected them. I started the engine and let it run in my garage for a couple of minutes and the light was off, I will test it better and longer next weekend.

One mine it was the rectifier in the alternator that became very rusty after 36 years and not making good contact anymore ..

[junkuser]

Yep Rob, wrong wording used, sorry.
Would have been more accurate to say "an output from the alternator", but still rather clumsy.

My only excuse is that having repaired alternators and modified regulators for many years I was thinking voltages rather than terminal naming.

For anyone I have confused.
                                           The feed to the lamp is from D+, which is the voltage generated in the stator windings of the alternator.
This is used by the regulator to to adjust the voltage in the rotor/field windings via the DF connection on the alternator to regulate the output voltage of the alternator as Rob said.

DF output is the AC output of the alternator rectified to DC via the exciter diodes to feed regulator and lamp.

Mal.

[stevegt6]

After some poking around and checking wires and what not based on the above replies, and other than adding another earth to the block, couldn't find anything out of sorts...

So, I decided to check the ign lamp itself - pulled the holder out and turned to position 2.... Nice bright light and goes out once started. Hmmm....

It seems it is just the red 'jewel' that makes it appear dim - will have to take speedo clock out and look further....

[kin74]

Quoted from WIMPUS

One mine it was the rectifier in the alternator that became very rusty after 36 years and not making good contact anymore ..

After three days and some km's, the light is on again. Need to re-check everything... 😲

[RobPearce]

Quoted from stevegt6

It seems it is just the red 'jewel' that makes it appear dim - will have to take speedo clock out and look further....

I had my Vitesse fail the MOT once for "main beam repeater not working". It turned out it was lighting up fine, but the rubber seal that keeps stray light (from the instrument illumination) away from the blue jewel had shrunk to the point where it completely closed up the tube from the bulb.

[Velocita Rosso]

Quoted from RobPearce

I had my Vitesse fail the MOT once for "main beam repeater not working". It turned out it was lighting up fine, but the rubber seal that keeps stray light (from the instrument illumination) away from the blue jewel had shrunk to the point where it completely closed up the tube from the bulb.

I know when my main beams are on,  when the oncoming drivers wince and the drivers up front smell burning neck hair....

[JohnD]

Quoted from kin74

After three days and some km's, the light is on again. Need to re-check everything... 😲

You took it out and it worked properly, back in and it's playing up.

That points directly to a bad connection +/- a bad earth.
Get out your multimeter, set it to stun continuity, or else resistance, and test the wires either side of the lamp.  Wiggle them about.

If there is a broken wire and a high resistance on either side of the bulb, or a short circuit, then the voltages across the lamp when the engine is running  will niot be equal and it will light, dimly.

John

[kin74]

Quoted from JohnD

You took it out and it worked properly, back in and it's playing up.

That points directly to a bad connection +/- a bad earth.
Get out your multimeter, set it to stun continuity, or else resistance, and test the wires either side of the lamp.  Wiggle them about.

If there is a broken wire and a high resistance on either side of the bulb, or a short circuit, then the voltages across the lamp when the engine is running  will niot be equal and it will light, dimly.

John

Last night I was in my garage to do some other tests... and the light was off again!
Definitely a bad connection as you guessed, now I just have to find it out.