Ignition light not on

[tonyabacus]

No problem till a few days ago when having turned on ignition the ignition light did not come but engine fired and ran. Tried again and after switching on there was a very very feint glow from the light but again engine started and ran. Anyone any ideas?
Thanks
Tony

[john.p.clegg]

either a wiring problem ...battery to ign switch via ign lamp to alternator...or earth.... or your alternator is on its way out...

John

EDIT:-

Tony
The ignition warning light really has nothing to do with the ignition of the engine,it just tell one that electricity is where it should be and getting to the alternator,and when it extinguishes that the alternator is producing at least the same voltage as the battery.

John

[billwill]

Test its bulb first.

[tonyabacus]

John/Bill - Thanks
Bulb already checked and ok and John the alternator is pretty new and last week the light was showing on strong as normal, so I had discounted the alternator, perhaps that was a mistake. Wondering now whether its an earth problem.
Tony

[billwill]

If you look at the internal circuit of an alternator which you see on thread:
http://www.lotusmarques.com/images/stor ... iagram.jpg

If you can follow such diagrams you can see that apart from external wiring error, the only thing likely to produce your symptoms is that the voltage regulator (the transistors at top left) have gone open circuit.

So check all the wires going into the alternator particularly IGN & F, regretably if they are ok, it would seem that your voltage regulator has blown.


Other discussion has said that if you were unwise enough to run the engine with the battery negative disconnected, modern alternators might produce excess voltage and blow the voltage regulator.

So you do need to check your earthing.

[YellowS4DHC]

Tony,
Given that the bulb is good and the alternator is new, I'd be inclined to check the ground connection of the ignition warning light before I anything else.

Use a volt/ohm meter to check the ground connection resistance. Or, simply attach one end of an 18 or 20 gauge wire to a known good ground and the other end to the warning light ground attach point on the back of the tach. If the light glows like it should when the ignition is switched on, problem identified.

If not, then you need to do some serious head scratching.

regards
Rick

'72 Europa TC
'69 Elan S4 DHC
'67 S800 Coupe
'57 T1 Speedster

[bob_rich]

Hi Tony

If you remove the lead on the alternator to the control (or field) the thinner of the two wires ( brown /yellow on my car) and touch it to the engine block for earth the ignition bulb should light when you switch on the ignition.
repeat the above but this time earth to the alternator body when you switch on the bulb should also light. This will confirm both the bulb, wiring and the alternator body earth are OK ( I assume the main earth is OK as you say it started the engine OK). If bulb lights then I suspect the alternator control module inside the alternator is at fault.

Hope this helps best of luck

Bob

[Andy8421]

Tony,
Given that the bulb is good and the alternator is new, I'd be inclined to check the ground connection of the ignition warning light before I anything else.

Use a volt/ohm meter to check the ground connection resistance. Or, simply attach one end of an 18 or 20 gauge wire to a known good ground and the other end to the warning light ground attach point on the back of the tach. If the light glows like it should when the ignition is switched on, problem identified.

If not, then you need to do some serious head scratching.

regards
Rick

'72 Europa TC
'69 Elan S4 DHC
'67 S800 Coupe
'57 T1 Speedster

Rick,

That isn't how ignition warning lights work on a Lucas / Elan set up.

The ignition warning light isn't earthed, it has two wires going to an insulated plastic bulb holder. One wire goes to the switched side of the ignition key, the other to the alternator.

When the ignition key is switched on, current flows through the bulb to the alternator and the bulb lights. After starting, as the alternator voltage builds up, current flow is reduced and the bulb goes out.

To the O/P, Bob's recommended checks (post above) are the way to go about testing the system.

Good luck.

[billwill]

[tonyabacus]

Thanks everyone for taking the time to reply, I will try Bob's suggestions, cannot get to the car for a few days but will report back as soon as I can.
Tony

[YellowS4DHC]

Andy,
thank you for the correction, I stand corrected (or sit, actually).

It is clear from the diagram that Bill posted that the warning light doesn't ground on the tach case.

Also, thanks Bill for posting the diagram.


regards
Rick

'72 Europa TC
'69 Elan S4 DHC
'67 S800 Coupe
'57 T1 Speedster