No ignition light or charge after alternator conversion

[Casiofi]

I've installed a new wiring loom, premade with alternator connections. When it was first put in, with just the engine connections in place, the ignition light came on when the ignition switch was turned on, the engine started and ran, the ignition light went out when it was running, and I was getting 14.5-14.7V at the battery.

Sometime between then and connecting all the lights/wipers etc, the alternator has stopped charging, and the ignition light shows no sign of lighting up at all. Frustrating having invested in a new loom etc, and this is the last hurdle before the car's back on the road after 18 months. And it was working! I've checked the connections to the back of the switch and at the alternator end and they all seem to be solid enough.

Apart from the alternator itself, and small wire from it to the light, is there anything else that could be causing it? Such as the solenoid? And is the ignition light circuit essential to the alternator charging as I understand it is with the dynamo? I am armed with a multimeter and many batteries for fault finding, just want to make sure I'm not missing anything obvious - any suggestions for checks to be made would be much appreciated. ESM are happy enough to exchange the alternator if it turns out to be the case.

Car info if required:
1969 1098cc with blackface speedo
ESM alternator kit and wiring loom, chassis number checked for correct dates for loom

[mogbob]

Are you still getting 14.5 / 14.7 volts when the engine is running , is the first question ?
A very simple check especially if we are talking about an original bulb in the ignition light....is , has the bulb " died ".

In the middle of a restoration it's easy to get worked up into "full blown problem solving mode " believing things are major
( and expensive ) to solve. You were right to take stock. I'm sure every contributor to the Forum has a "what was I thinking of " moment to recall.
Bob

[IslipMinor]

In most cases a working 'ignition warning light' is essential to getting an alternator to charge. It can be possible that some residual magnetic field will be enough to excite the system, but not to be relied on.

The voltage supply from the ignition warning light provides the initial power to the rotor that initiates the charging process. As the alternator speed increases, the supply to the rotor is from within the alternator itself, as it becomes 'self-sustaining' and is controlled by the regulator to provide the appropriate output voltage to the battery.

If you turn on the ignition, are you getting any voltage at the small alternator terminal?

[bmcecosse]

Did you convert the car to -ve earth??? Where did the alternator come from - there have been some poor reports of some suppliers' alternators.

[simmitc]

The post does say that it came as a kit from ESM. I've not had any duff alternators from them. My first thought was the earthing as well.

[bmcecosse]

I think others have had a problem - specifically there. But no response to the earth request

[Casiofi]

When the engine is running I just get 12v ish over the battery, which gradually reduces while the car is running until there isn't enough power to keep the engine running - the alternator isn't charging at all.
I measured the voltage from the small terminal when the problem first occurred, and as I recall I had about 3V - I'd need to double check though. Does that seem low?
BMC, the car is -ve earth, converted by the previous owner - knew there was something else I meant to put in the first post!
Right now, I'm going on the basis that the ignition light not lighting and the alternator giving no charge are linked. What I'm trying to figure out is whether the alternator is faulty and causing the ignition light/circuit to not work, or whether there's a fault in the ignition light circuit that's causing the alternator to not charge. I'll be back home to do some fault finding on Thursday, so if I haven't figured it out I'll post various readings up here.

[bmcecosse]

None of my Lucas ACR alternators every needed the Ign light to work - but I guess perhaps the newer ones do. So the main thing is - have you wired it up correctly - have you removed the control box? Follow the simple diagram near the top of this section.

[Casiofi]

I'll post some photos of the wiring tomorrow - the loom came prewired with the alternator plug and completely bypassed the control box, thus it hasn't been refitted to the car.

[oliver90owner]

If the fault is with the alternator, it is likely a sticking brush.

[bmcecosse]

So how did the 'pre-wired' loom' intercept the Ign light connection ??

[Casiofi]

I'll have to update you on that one tomorrow or Friday - can't remember off the top of my head!

[IslipMinor]

We are assuming that the alternator is a Lucas ACR or later similar version - is that correct?

If so, this is the basic charging circuit for the Lucas ACR and later similar alternators:
[frame][/frame]
I have added the standard Lucas/Minor wire colours. From the BMC Workshop Manual the main feed to the battery is shown as yellow then brown/yellow for Minor dynamo and brown/white for Minor alternator.

The Lucas ACR range usually has 3 output terminals - 'Ind' and 2 x '+'.

The 2 '+' terminals are connected together in the alternator and should always read battery voltage - if not there is a problem with the wiring between alternator and battery.

Disconnect the plug from the alternator and connect the small terminal to earth - NOT either of the large ones, as they are connected to the +ve battery terminal! With the small terminal 'earthed', switch the ignition on and the warning light should illuminate - if not fix this first. Check to make sure that the warning light has not fallen out from behind the speedo - it can happen.

Whilst the plug is disconnected, check the main feed from the alternator to the battery circuit. If there is one 'large' brown/yellow or brown/white (or whatever ESM have used) wire running from the alternator to the battery, what voltage do you get from that to earth? Is it the same as the battery voltage? If there are 2, then check both.

If all OK, do you live near anyone who has a known working Lucas ACR alternator that could be swapped to test your wiring?

[bmcecosse]

And perhaps risk burning out the swapped alternator if the wiring is wrong.....

[Casiofi]

Bit of an odd couple of hours. The ignition light is now working - comes on when the ignition switch is in the on position but the engine isn't running, and goes out a few seconds after the engine has started. When spinning the alternator is making a slight whining noise that it wasn't before. The voltage over the battery with everything off is 12.6v, with the engine running is 12.7v which still seems low (I'm expecting 14v+ over the battery if everything's working correctly). I haven't rewired anything, just took the plug off the alternator a couple of times to do continuity checks, then after everything was reconnected and the engine had been running for half an hour or so the alternator started whirring and the ignition light started working as it should. Bizarre but there we are.

The plug for the alternator, top (small terminal) to bottom, is: Yellow/Brown, Thick Brown, Brown. All three appear to be connected as per the diagram above, so I don't think any replacements will be fried!

Yes, it is a Lucas 18ACR type alternator. Very useful diagram and test procedures. I checked both the battery connected terminals on the alternator plug as suggested, and both gave the same reading as straight across the battery - so the wiring to the alternator plug is fine? I do have a neighbour with an MG Midget with the same kind of alternator, but he's away until Monday. I've contacted ESM and they've sent out another alternator, so by Monday when I'm next free to work on it I should have two others to try.

[IslipMinor]

Do you have any of these scenarios (all assume the engine is running at a reasonable speed, the fan belt is fitted and adjusted correctly and the alternator connections are correct):

Engine running, ignition light on, no charge, no alternator whining - ?alternator fault, NOT brushes (connection through rotor is OK)

Engine running, ignition light out, bulb is GOOD, no charge, no alternator whining - ?alternator fault, brushes?

Engine ignition light out, charge, alternator whining - normal alternator charging state!

From what you have said, if sometimes it does charge and sometimes not, as has already been suggested, a sticking brush could be the problem. This should not be with a new alternator, so it will be interesting to see what the replacement one from ESM does?

[bmcecosse]

You still don't say where you intercepted the warning light feed..... I'm amazed anyone is still supplying new ACR alternators..... Whirring noise doesn't sound good......but you are by no means the first to suffer dodgy alternator from this supplier.

[Casiofi]

New alternator fitted and appears to be working - many thanks IslipMinor and bmcecosse for all the help! I'm getting around 13.5v at idle and 14.2-14.5v with the revs up, which seems fine to me. The lights certainly stay bright while driving!

IslipMinor, it was the second scenario you described that I was having - sometimes with the alternator whining and sometimes with it not. Still not entirely sure what the fault was but the old alternator is being returned to ESM, it may be something simple like a brush or something more serious. But regardless, I think a spare alternator might be a worthwhile investment, just in case.

BMC, I'm not quite sure what you mean with regards to the warning light?

[bmcecosse]

Well done. I was asking how the alternator wiring connected to the warning light wiring - but since it's all working now, it doesn't matter. you really don't need a spare alternator - I carried one for years , and never had to use it...

[Big Jim]

I think I have the same symptoms . Same sort of readings with ignition off / engine running . The alternator does seem to be doing something , if I turn on some lights etc , the voltage drops and comes backs comes back to about 12.6 volts . I am not sure how good my battery is so I have a new one on the way .