Ignition light

[tractorjames]

Ill probably get slated for this post, but ill give it a go.

I have a mate with a MG BGT ??) And the ignition warning light stays o. while running. Although it does get dimmer when running/revved up.

The bulb is the same bulb as before the problem occurred.

The battery seems charging fine. 14v + at battery when running. I do need to do a test with all the lights etc on.

With the ignition on there is 12v coming down the small brown wire from the light.

The connections are all clean, emeryed them up WD40 and reassembled.

I have a feeling that the alternator could do with a rectifier/diode pack putting in it but could anyone give any suggestions.

Cheers,
James

[TedTaylor]

Almost certainly diode/regulator problem - the way the light is behaving are classic symptoms.

Replacement diodes/rectifiers are available but make sure that there is no wear anywhere else before going the the time/trouble/expense of this job.

[junkuser]

As the lamp filament is between the output of the alternator and the loom of the car, the voltage of both sides has to be very close to the same for the lamp to extinguish completely.

You mention 12V from the lamp connection James, but what is it with the engine running, on the loom side of the lamp?

Resistance in the loom connections between the battery and the lamp, including the ignition switch, can cause sufficient voltage drop to get some illumination from the lamp.

[tractorjames]

Thanks both for your replies.

Ill go up this weekend  then and do some more testing  :)

Thanks again,
James

[bodders1]

Alternator on the way out.  
Reconditioned Lucas ACR series alternators are cheap enough on an exchange basis from pretty-much any motor factor not to bother with the aggro of sourcing the rectifier/regulator components and then attempting a home repair only for another part of the alternator to fail in a few months time.

On the other-hand, since it's an MG, just scrap the car ;-)

[yorkshire_spam]

Dunno about trumph alternators, but a dim/intermittent charge light experience on a Land Rover (about 3 times over the years) always led to what appeared to be a working alternator packing up within about a month of every day usage.

[WIMPUS]

James,

My friend bought a MG B Gt  :X last week ! and has the same problem, ignition light stays on ..

Yesterday the car passed his test her and on the way back all the electrics failed and after 2 sec's it was back on ..
So stopped at a parking and i could hear a grinding noise  :-/

Then he got the car off and it wouldn't restart .. so i looked how much volts there was on the battery and it was under 12volts  :-/
After 10 min we had a try to start it again and then it gave 13,40 volts ..
But i guess not enough for when the lights, radio & co are on ..

Maybe going to look at it this afternoon  :)

Wim

[WIMPUS]

4526 wrote:

James,

My friend bought a MG B Gt  :X last week ! and has the same problem, ignition light stays on ..

Yesterday the car passed his test her and on the way back all the electrics failed and after 2 sec's it was back on ..
So stopped at a parking and i could hear a grinding noise  :-/

Then he got the car off and it wouldn't restart .. so i looked how much volts there was on the battery and it was under 12volts  :-/
After 10 min we had a try to start it again and then it gave 13,40 volts ..
But i guess not enough for when the lights, radio & co are on ..

Maybe going to look at it this afternoon  :)

Wim

My friend also told me this afternoon , when i put on the lights the ignition light burn's a bit brighter ..

[tractorjames]

Thanks for the replies. im definitely going to repair it though. (agricultural engineer by trade) i dont think ive ever had to buy an aletrnator. you can get regulator, rectifier, brushes and bearings for £20 and with all that and cleaned up slip rings theres not much else to go wrong  8)

I was really wanting to see if people were certain on an alternator fault rather than wiring.

Loving the scrap it comment  ;D

Cheers,
James