Ignition warning light comes on when I rev!?!

[moredoorconvertible]

Finally got around to sorting out the ignition warning light on Betty after having a flat battery and now have the following problem.

When I start the car the ignition light stays off. As soon as I drive and build the engine revs up the light starts to glow. Once it is on it stays on until I leave the engine at idle for a few minutes and then it goes out again. as soon as I increase the revs it comes back on?

Is it a voltage regulator problem or the dynamo?

Gary

[bmcecosse]

Have you swapped the polarity of the car by any chance - even accidentally ? Is the fan belt very loose ?
To diagnose fully - when you first switch on the Ignition - does the light glow ? Then you start up - and as the engine idles - the light goes out ? Then as you rev up - the light glows again - is it bright - or just dim ? Final check - do this in the dark - start up and let it idle - switch on the headlights so they are shining on a wall - then rev up - do the lights get brighter ?

[Alec]

Hello Gary,

it may well be the regulator, I had a 17ACR fail exactly like that and it was overcharging. If you have a meter you can soon check or as BMCE says if the lights go brighter then that's the probable fault. Another clue is if the battery area smells of sulphuric acid?

Alec

[bmcecosse]

The light just works as a voltage detector when used with an alternator (but I'm guessing you have a dynamo) . It shines if there is higher voltage at one end than the other - and it doesn't care which end is higher - as long as there is a difference - current will flow and the light will glow. (I'm a Poet now!) So - I suppose IF the alternator was running really high volts - and the battery couldn't soak it all up - there would be a difference and the light would glow. But I suggest that's a very unusual failure!

[Alec]

Hello BMCE,

oops, I missed the reference to the dynamo earlier.

The thing to do is as suggested earlier, try and find out what is happening, diagnose and rectify.

Alec

[mike.perry]

Take the top off the control box. When you rev the engine the contacts on the cut out should close then open when the revs drop. If they do not then check the fan belt tension then check the dynamo brushes

[moredoorconvertible]

Checked the fan belt which is fine and 'flashed' the small terminal of the dynamo against the non earthed side of the battery just in case! Still the same.

When I switch on the ignition the light glows bright, start the engine and the light goes out, build up the revs and the light starts to glow but is very dim, let the revs drop and the light goes out again! When driving the light gradually gets brighter but does flicker every now and then.

Last night I put the lights on and revved the engine whilst the ignition light was glowing and the brightness of the lights did not change, this morning when I got to work I did the same thing again but this time when the ignition light was out. As soon as I revved up the lights got brighter and the ignition light started to glow again.

Mike, I will have a look at the control box at lunch time to see what that does.

[bmcecosse]

Well - since it seems your dynamo is able to produce a charge - the lights do get bright at times - it would indeed seem to be a problem within the control regulator. You can try cleaning the contacts with very fine wet/dry paper - just pull it through between them.

[pjw]

I know this is a perhaps a bit late but we've just solved the same problem. It would take several pages to relate the whole story but the bottom line was bad earth connection.

Simplest solution was running a separate earth wire from the E terminal on the control box to battery earth. Everything worked perfectly after that and it only took three of us six hours to work it out!

[bmcecosse]

Well done! Thanks for sharing with us.

[Rob_Jennings]

can indicate that the brushes and contacts in the dynamo are very worn or/and that the bearing in the dynamo are shot.

Had this fault in the mini:
at low revs the dynamo worked ok producing a reasonable charge, but as you spin it faster the charge level drops (so the light starts to come on esp. with extra load like lights). external regulator box was fine.

eventually the bearings in the dynamo gave up and it was game over (switched to alternator at that point)

so at low speed the brushes happily 'tracked' the contacts and the 'wobble' cause by bad bearings but at high speed I assume they start to 'hop' over some of the contacts.

what can you do.....
1: remove fan belt and check for movement in the dymano pully if there is a lot you probably looking at worn bearings and a new unit (you need to oil it regularly with a drop light oil e.g. 3in1)
2: if 1 is ok then renew the brushes and springs, be sure to clean the contacts inside (very fine paper and turn the dynamo by hand, remove paper and blow or hoover out rubbish again turning by hand)

[DaisyMayFozz]

mine used to come on and it was down to a fauly voltage regualtor box, which then caused a electrical fire........ cost me a fortune just for a red light