Ign light on after switch off?

[epcot_pete]

Hi All,
Have done what Tony asked.
Tidied wiring up roughly until problem is solved, but at least all connections are clean and tight.
Connected separate large wire from middle spade connector on alternator to starter solenoid also large brown wire is connected there instead of battery.
This large brown wire is connected to large brown/yellow (to alt); large brown/white (to light switch) also small brown/white (to ammeter), so all connected together with good contact.
Small brown/yellow (to ign light) is connected to small brown/green (small terminal on alternator).

So connected battery and switched on ignition key. Only oil/choke/hand brake light came on in dash cluster?
Started motor fine and ign. light in cluster came on, but 'pulsated' (on, then slightly brighter, then slightly dimmer and so on), rev'ed a little with no change so turned off.
Switched key on and this time ign. light on cluster came on - so normal cluster lights.
Started motor and again ign. light 'pulsated' and no change throughout rev range and no change when all lights/heater/wipers etc were switched on.

Do you think I ought to but a new alternator?

GrahamC suggested removing the ammeter, think he meant disconnecting it so gauge is still there but not doing anything. Should I disconnect the ammeter?

Sadly I do not have an voltmeter.

Thanks for all your help, wiring is not my best point!
Pete

[MIG Wielder]

Hi Pete, Thanks for the update. The wiring sounds O.K. now, but its curious there are apparently 2 faulty alternators. I'd be very interested to measure the voltage on the White wire to the IGN light and compare it with the voltage on the small IGN light terminal and then the battery voltage. And again I would have expected the ignition light to be much brighter with all the electrics on.
Sadly I can't explain the cyclic lighting of the IGN light.
But something that is interesting is that the IGN light did not come on the first time you operated the key.
Assuming there is no dodgy connection in that wire the reason would be that one or other of the carbon brushes in the alternator is sticky or worn right down. ( See Dolomite Sprint manual page 86.11 for the diagram).
Stating the engine rattles it around and it makes (intermittent?) contact again.
So yes, I'd have it out and change the brush pack.
And yes I'd leave the ammeter in for now as it looks like its basically working.
Tony.

[epcot_pete]

Hi Tony,
Thanks for advice and I have ordered new brushes.
I am away for a couple of weeks and will let you know result when I get back.
Pete

[grahamc]

Hi Pete,

It sounds like you've made some progress.

I only removed the ammeter as an alternator can put out more current than a dynamo and I had access to a free stack of gauges to replace it with. So my 3 instrument cluster now has fuel, temp and an oil pressure gauge.

I simply joined the ammeter wires together behind the dash, but as long as the gauge isn't going off the scale it should be ok.

Good luck with the new alternator brushes.

Cheers Graham

[epcot_pete]

Bought new brushes and had five minutes to fit them today before going away. The old ones were just slightly shorter than the news ones and were free moving, so put new ones in anyway. Alternator with black plastic cover removed looks normal, no loose wires or signs of burning etc.
Put it back on and switch ign, on and no red ign. light? Started immediately and red ign. light comes on, not very bright and slightly pulsating. Makes no difference in rev range or headlights/heater/wipers on.
If I connect the small brown/green wire from back of alternator (goes to ign. light) and connect to 12v, the ign. light is its usual brightness so no problem with the wire or bulb in the cluster.
The ammeter shows no sign of movement, so should I disconnect it and buy a new alternator?
Back in a week and a half.
Many Thanks
Pete

[MIG Wielder]

Hi Peter, That was quick ! Our local "xxxx" Main Agent could do with people like you.
Something that isn't right is that disconnecting the wire on the small terminal and connecting it to +12V should leave the bulb still off. Its connecting it to 0V (or earth) that should light it.
I shall think on this after supper.

Don't worry; we can solve this.
Tony.
Edit 7/10/17 : If the Ignition is OFF when you remove the thin wire from the alternator and connect it to +12V then yes the Ignition light will light as current can be fed in reverse through the bulb, through the low resistance of the coil and back down to earth through the points ( or any other electrics that are left switched on ).
Can you try the same thing please with the ignition ON and the thin wire IGN light connected to a good earth.

2nd Edit 9/10/17 : If the above test works that means if its not brushes ( the cheap bits) then the internal voltage regulator is faulty or the small diodes in the rectifier pack or the field winding is dodgy. Which are the expensive bits so as has been suggested... a new alternator will solve it.
Thanks,
Tony.

[epcot_pete]

Hi Tony,
Returned from holiday to find new alternator sitting on doorstep so fitted it today - absolutely perfect!
Everything works as normal so very pleased and thanks to all for reply's.
I now have two alternators which are no good and need one for the MGB. On eBay you can buy a rectifier for £20 ish, is it worth buying one of these to refurbish one of the old ones or but a new one?
Thoughts please?
Pete

[dollyman]

Personaly i would just buy a new one as they seem cheap on ebay, and non exchange
I know it takes the fun out of repairing an item Maybe its me getting lazy in my old age
I know Tony (mig welder) would repair, but he is an expert in electrics Where as i am not
Cheers, Tony.

[GTS290N]

Those old acr alternators were crap in the day, and they're crap now. Get a new one.
Or replace the diode pack, the slip rings, the bearings.....

[MIG Wielder]

Edit 7/10/17 : If the Ignition is OFF when you remove the thin wire from the alternator and connect it to +12V then yes the Ignition light will light as current can be fed in reverse through the bulb, through the low resistance of the coil and back down to earth through the points ( or any other electrics that are left switched on ).
Can you try the same thing please with the ignition ON and the thin wire IGN light connected to a good earth.

Tony.

Hi Peter, Its good that its sorted. Did you get a good result with the above test ?
The trouble with replacing alternator parts to get them working is that its like eating salted peanuts: you can never eat just one.
So after you have replaced brushes, regulators, diode packs, and find you have a faulty field coil, if you have several cars all with the same Lucas alternators you can save the good bits and put all the faulty bits back into one unit and service exchange that one
Yes, probably best to bite the bullet and get a new one.
Tony.

[epcot_pete]

Sorry Tony,
When the new one arrived, I just fitted it without doing the check as you requested so no result - sorry!
The other comments are correct insomuch as just buy a new one. I come from a day when money was tight and I was the youngest of 5 brothers so watched them working on their cars each weekend just to keep them on the road, so repairing/bodging things was the norm.
We had a shed with loads of old bits and when there was a problem, it was raided to rebuild parts. It was good learning which is often missed in todays throw away society, anyway that was the past and I have my car back on the road.
Thank you ALL.

P.S. What a great club this is for help and advice!