13 replies to this topic

[Brown Mini]

Hello everyone

I fired up my resto - at last - all's good but my ignition light stays fully on - it doesn't 'rev' off

The fan belt is a new one - A tiny bit loose but not anything major

...does this mean my alternator is trashed - How can I test it?

[dklawson]

There are only a couple of tests you can carry out at home. With the engine "off" measure the voltage across the battery terminals. Start the engine and repeat the measurement. You should see an increase of 1 to 1.5V with a maximum voltage of around 14.5V with the engine running.

Beyond that, your easiest/best bet it to take the alternator to a parts store which should be willing to bench test the alternator for free. They may not be able to tell you what is wrong but they will be able to confirm if the alternator is working or not.

[Brown Mini]

Thanks for that ... so am I right to think that that's the only cause of my IGN light on ? A dodgy Alternator

[dklawson]

I am always learning new things and to each rule there is an exception.

Since the belt is new and presumably correctly tensioned I cannot think of any other simple answer than the alternator needs to be bench tested. It could be something as simple as needing new brushes or it could be that something in the regulator circuit has failed.

[Brown Mini]

Hi all

I tried this today and there was no change in voltage - so I guessed the alternator had failed - i changed the alternator and it didn't make any difference

So there is no charge back to the battery - any ideas what I need to check next ?

[dklawson]

You said you changed the alternator. What/where did the "new" alternator come from? Was it purchased from a supplier, a salvage yard, taken off a running car? In short, do you know that the alternator you just installed is/was working before being installed?

There are a couple of tests you can make. First, unplug the alternator from the loom and turn on the ignition. If the warning light comes on... you've connected something wrong during your restoration. The warning lamp circuit uses the alternator field coils for an earth connection. So unplugged, the warning light should never be able to come on.

If you have a multimeter there is one other simple test you can make. With the engine off, unplug the alternator. Use your multimeter and measure the voltage between an earthing spot and each of the big lugs in the alternator connector on the loom. You should find battery voltage on the big wires going to the alternator. Let us know what you find.

Turning back this thread to its start I guess some other questions need to be asked. You said this was a restoration. Did your restoration work involve the wiring? Did you fit a new loom or is it an old one? The ignition light circuit should take power from the ignition switch, run it through the red warning lamp, then go off to the small lug on the alternator. I encourage you to look at your wiring diagram for the proper colors and confirm that you have the correct wires from the switch to the alternator.

Here's what's supposed to happen:
1) Engine off, ignition key turned of = no power to the alternator field coils, warning lamp off.
2) Engine off, ignition key in the run position = power flows from switch, through red warning light, through alternator field coils, to earth. Warning lamp is on.
3) Engine on, ignition key in the run position = alternator starts making power, part of this power is "fed back" to the small lug on the alternator where the warning light connection is. This means both sides of the warning light are now at charging system voltage. With no difference in voltage across the warning lamp... it turns off.

[alicetheauto]

Try running a voltmeter or test lamp from the wires in the back of the alternator plug (cant remember which of the 3 it is...) to earth. It should read 14v ish, or at least light up. If not then you still have an alternator issue. Obviously the car is running.... Is this plug intacct? The wires can pull out easily.

[Brown Mini]

Thanks for the full reply - I will try all of these

Yes I have played with the wiring and the IGN light did come on without the alternator being plugged in

The other alternator is a used one so not sure of it's background - neither threw any charge back to the battery - both sat at 12v with engine on and off

I'm now wondering if I've been confused with oil pressure light and IGN?? The wiring was in a right mess so anything is possible

I will try out these possibilities and update the thread - thanks for your help

Andy

[dklawson]

I would say there are some wiring problems to sort out.

When you unplugged the alternator, the charge warning light should not have had an earth connection and therefore... should not have turned on.

Equally troubling though is IF you did swap the oil pressure and charge warning lamp wires... why was the oil pressure light on?

Tackle one problem at a time. Oil pressure is critical, charging isn't. Sort that one out first (starting with the wiring so you know what you're really looking at) then back to the alternator!

Keep us posted with your progress.

[ashby_steve]

i spose youll soon see if your battery runs out lol

start your car , lights, stereo leave it all on for a while, when my alternator went i had to charge my battery about 4 times in the space of a week

untill i could afford it lol, if your car has held its charge and its being used daily maybe its something else?

just spit-balling a few ideas mate

[dklawson]

i spose youll soon see if your battery runs out lol

if your car has held its charge and its being used daily maybe its something else?

Unfortunately there is evidence that the alternator is not working. Brown Mini has already measured battery voltage with the engine off and with it running, both conditions measured 12V. That means the alternator is not producing any power and his battery will run flat. You can drive a car for many miles on just the battery. The more starts you make and the more accessories you run, the shorter the distance you can drive, but many miles are possible when the battery starts from a fully charged state.

The fact that the charge warning light comes on at all with the alternator unplugged indicates a wiring problem that has to be sorted out.

[Brown Mini]

Hi Doug

Ok - I've isolated the oil pressure and wired a light in from scratch so that's all good and works fine (IGN light still works)

Looking at the loom - I haven't touched the harness around the speedo (Centre Speedo - it's a 1980 classic front) and it's all the original wiring but when I wired it all up there was no alternator as the engine was out but I defo had a light come on when IGN was on so I assumed that would be IGN - it's defo not oil pressure as that would need to be earthed through the sender wouldn't it?

I'm wondering if there's some wire mix up at the solenoid as the brown wires in the multiplug obviously can't get mixed up
From memory there's a white and red wire bang in the centre of the solenoid and a brown one to the right (as you look at the front looking back) (under the main battery feeds) could these be wrong ?

Really appreciate the help

Andy

[dklawson]

As hard as it is to imagine that a car as "old" as 1980 is too new for me to comment on... it is. I've never worked on the wiring of a car that "late".

Regardless, I can comment that there must be something amiss with the wiring but I don't see it being anything associated with the solenoid wiring. The ignition warning light should have something like a brown/yellow small wire leaving and going off to the small terminal on the alternator. With the alternator unplugged there is no way the charge warning light should ever turn on as the light will have no earth connection. What I'm trying to say is that you should be carefully confirming your basic wiring against an appropriate wiring schematic. If the wiring appears correct, perhaps the wire has a break that is making a short circuit to earth.

You asked about the oil pressure and yes, that lamp would get its earth connection through the switch/sending unit. It's basic operation is switched power from the ignition switch, in/out the light bulb, to the pressure switch on the block, to earth. The sending unit is normally closed and opens when the pressure reaches a minimum level.

The other solenoid wires you're asking about I can't comment on. I suspect they are all part of the starter relay and solenoid wiring used on the pre-engaged starters. Others will have to confirm that. However, they should only be "hot" when the key is in the start position and should not be part of your problem.

[Brown Mini]

Hi Doug

Quick update for you and anyone else with alternator issues

After following your last post I traced the problem to the wrong wire as my ign light. The loom on my resto was in a sorry state but the problem was from the harness that goes to the back of the speedo. I think it was theoil pressure wiring and was earthing through the speedo casing

So after continuity testing from the alternator I swapped to the correct wiring (the brown and yellow) and the ign light went out after starting the car

It was quite a simple fix in the end but couldn't have done it without your advice

Thanks very much, much appreciated

cheers
andy