Morris Minor Owners Club

I have changed over my negative earth 1966 Morris Minor from generator to alternator according to the instructions on MGAguru site.
http://mgaguru.com/mgtech/electric/ac101.htm

I left the control box in place and used it as a terminal for all the wires. I used a 16ACR Lucas alternator, which I had taken from my wife’s scrapped Mini years ago and which I knew to be in working order. The big brown wire on the control box terminal D is left unconnected an taped off at the control box end and at the alternator side. Instead I have connected a separate fat red wire from the alternator to the big terminal on the battery side of the solenoid.

The problem that manifests itself is that when I have connected the Ctrl Box F&D wires together away from the Ctrl Box (ign warning light and wire to alternator small terminal) the charging light glows dim when the engine is running at any speed. I can see by the voltmeter between the battery terminals that the alternator is not charging (12.5 volts)
If however I put the two wires mentioned above together on terminal D of the control box, there is a healthy charge of 14.5 volts at the battery with the engine running and the ign warning light goes out.
However when I stop the engine and remove the key, the ign. warning light stays on. This is a phenomenon the MGA guru describes as some problem inside the control box that keeps the cut-out relay contact connected. Momentarily blipping the starter extinguishes the light. I can live with this for now though, knowing the alternator is functioning correctly..

Has anybody got an idea why the alternator is not charging when the two wires are connected away from the control box and is functioning OK when the wires put together are connected to terminal D. Could it be an earthing problem, if so where? The alternator itself is earthed through the engine if I am correct or am i missing something???

I can't imagine why you are joining these wire together - the control box relays should be taking no further part in the action. Your red wire is correct - you need to join the wire from the Ign light (and yes -it used to go to the D terminal, but it's only a small diameter wire) directly to the small terminal on the alternator. Don't join it to anything else! See the alternator diagram at the head of this section.

the acr alternator is a simple one,take the black cover off and you will see the control box attached to the end of the alternator, its a silver box,it should have two wires one black(earth )and one yellow which goes to one of the contacts which holds the brushes. You can get new control boxes for about £5 off e bay(Just done one one mine) so long as you have small enough sockets to take the studs off you can do it in about 10 minutes.Whilst your at it if you have a meter check the flow accross the diodes in the rectifier pack,again simple. there will be three metal plates and you can see the diodes fitted through these plates simply check that the diodes are only alowing a current one way if you get a reading showing a flow both ways on any of the diodes then retifier pack(£10) will need replacing (Just done one on mine again off e bay) certainly better than £50 for exchange alternator .And yes the red light problem,was exactly the same as mine,dim with the ignition on and just sudenly charging at random>I dont know for sure that what you are doing would cause the same but you can bypass the control box and the alternator will charge at full charge regardless of the control box but it will eventually blow the battery so I wouldn;t do it again.Can't remember now but there was a way of bypassing the box to check the alternator output but should only be done for a few seconds,i think some have a small connector for this test.It could be that you are replicating this test. Good luck

The reason I connected the thin brown/green wire from terminal F to the Brown/yellow one on terminal D, was to serve as a direct link between ignition light (formerly connected to D on the regulator box) and the NG wire (previously on F) to the small terminal on the alternator (previously the dynamo).
To test the system and see if the NG wire was defective I temporarily substituted it for another one to run from the NY at the regulator box straight to the small terminal on the alternator, still not charging. Maybe it is an internal problem as Kennat suggested.
Am I right in thinking that, by keeping the wires connected to the old control box, it will still function and act as a protection to keep the battery from being overcharged by a faulty internal regulator?

I can see that you guys know so much more about electrics than I.
I am just following instructions here and hope everything functions as it should.

NO! The old regulator takes no further part in the proceedings. It can be kept there to look more original - and to act as a handy terminal block for the various wires - but keep the alternator wires well away from it. Connecting as you have done 'should' be fine - but don't do it at the regulator - just join them with a bit of choc-bloc. In fact my ACR16 charges fine without the small wire being connected - it works perfectly well - balanced headlights when on and so forth. I know this because it broke off at the connector - but i could see from my ammeter all was well. I left it like that for a week just to see what happened - absolutely nothing! It worked fine.

have a look here http://econofix.com/alt.html all you ever wanted to know

That's a really comprehensive link with lots of useful info. That should keep me busy for a few days ....
It's winter in Holland now with snow and temperatures down to minus 11 at night. So work on the car has stopped for now, as it's too cold to hover about outside in the dark after work.
Oh well, plenty of time to read up on things. Thanks for your help so far.

Although it has been a couple of montghs I thought it only fair to tell you that everything now works as it should.
The problem has been solved. It turned out the 16ACR alternator was not as perfect as I thought it would be. After I replaced the internal regulator and rectifier pack (diodes), the ign light now comes on when turning the key and goes out when the engine fires and charges the battery at a healthy 14V. When removing the key from the ignition the light goes out.
Thanks all for your help

Great success.......