11 replies to this topic

[riczito]

Hi all.

 

I have a 1994 1275cc carburettor model. I have been struggling to diagnose a flat battery issue. It's been unable to start the car twice recently after long journeys. Initially I thought it was the battery itself - but it's less than a year old so that seems odd - then I suspected the alternator. This morning I reinstalled a fully charged battery to start doing some tests, and noticed that when I turn the key the ignition light isn't coming on. I never noticed this before, probably because the radio lights up like a Christmas tree and that distracted me. Anyhow, I've been reading up on this and it seems that innocent little light is actually critical to the charging circuit.

 

My question is : if the bulb is blown, can that actually stop the alternator from working? Could that bulb be the cause of my issues?

 

Many thanks!

Ric

[lordcakes]

Yes, if the bulb is blown then there is no current flow in that circuit which is the very thing that tell the alternator to produce a charge.

Check the bulb and test again. If you have a multimeter, a good fully-charged battery should be at around 12.6 volts. With the engine running you should see at least 13.8 volts and usually more.

[riczito]

Brilliant, thanks for your help. My battery is giving 12.93 volts. I haven't tested it with the engine running yet. I'll wait till I've fixed the bulb. I'm sure that will be fun - it's almost completely inaccessible, as I have installed a wooden dashboard with fitted gloveboxes. I may need one of my kids to slide their hand up underneath to undo the dashboard wingnuts. Ha ha, life with a Mini! 

Edited by riczito, 30 September 2021 - 07:26 AM.

[Ethel]

Remove the alternator plug & connect the brown/yellow to earth. The turn on the ignition & see if the bulb lights. Assume other ignition fed stuff (oil light, fuel gauge) work?

[panky]

And just in case you're thinking about an upgrade don't be tempted to replace it with an LED, it won't work.

[Spider]

And just in case you're thinking about an upgrade don't be tempted to replace it with an LED, it won't work.

 

I have done this many times, but fitted a shunt resistor across the LED.

[floormanager]

Going back in years but the only time I've not seen the ignition light on means the alternator is gone.  Happened to me a few times.

[Miki Leyland]

Excuse me for rescueing this, but my IGN light does not turn on either and the car starts normally (I thought it was not possible without the light). The car has an alternator.

Following this thread, I've checked the battery and it is not charging.

 

My question is: It the alternator definitely gone (it has only 1 year) or could it be that it is not charging just because of the bulb itself?  Coincidentally, yesterday night I was lubricating the speedo cable behind the center clock and it is precisely this morning when the bulb is not working.  Maybe I moved some of the wiring in the bulkhead that could cause the alternator to not charge?

 

Thank you in advance.

 

[lsto]

Check the bulb first. It won't charge if the bulb has failed, also it's a lot cheaper then a new alternator. If that doesn't work I'd check you haven't disturbed any wiring behind the dash before jumping to the alternator.
Good luck.

[Ethel]

The bulb should be insulated from the speedo housing. It's possible it might be earthing if you disturbed it. The illumination bulb holders are metal & earth (also high beam), the other warning lights should use plastic bulb holders.

[Spider]

If you disconnect the Brown / Yellow wire off the back of the Alternator and short that wire to Earth, turn the Ignition Switch ON, the IGN Lamp should light up. This will test the wiring and the bulb.

[Miki Leyland]

Thank you all for your tips. I'll try to check all these tomorrow.