I wonder if the box you describe is a Control box from when the car originally had a Dynamo (I trust you checked it’s not a fusebox holding its fuses), conversion to alternator is a very common and sensible thing to do with older cars.
The control box in this situation is usually defunct when converted …but not quite.
Trouble is can’t recall precisely what year Minis went from Dynamo to Alternator. All mine were originally dynamo (late 60’s and early 70’s) and I had a problem with the car cutting out (a 1969- first year of clubman manufacture - Clubman estate cutting out when I applied brakes and thus inturn activation of brake lights, I traced to a broken connection/tab on/within the Control box.
Now the following is an article from converting a Min from Dyno to alternator and the reason I include it is because the section on the control box might be relevant (as I said although now dynamo the CB still has to have a couple of connections made – so to speak) and thus these MAY have come loose/broken.
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Article: “
The following procedure is the way to carry out this conversion on a Mini. The procedure will be pretty much the same for all late 1960s and early 1970s British cars (I.E. Ford, MG, Morris Austin, Rootes)
Fitting an alternator will make the car more reliable as the AC current from the alternator is more stable than the DC from a dynamo. This conversion also makes the sometimes unreliable control box redundant.
Converting the car to negative earth will allow you to connect modern stereos, electronic ignition, modern fuel pumps etc. Also because of the way the electrons flow the car will not rust as fast!
Another point to consider is while fitting an alternator increases the reliability it removes some of the originality. This could affect the price of the car.
What you need:
An alternator. Lucas 16ACR (Or similar recon) is probably the most suitable. 18ACR and 20ACR will fit too but because they generate higher current they may cook the wiring!
Alternator terminals. Supplied with genuine new Lucas alternators (& reputable recon ones)
New battery earth cable. Only needed if the existing earth strap doesn’t reach the negative side of the battery.
Alternator mounting bracket. From Mini specialists (expensive) or from any scrap yard Mini/Metro (Cheap)
New fan belt. Not essential either but worth changing given the price of a new one. Remember the 850-1000 fan belt is shorter than the 1100-1300 one.
Check the vehicle polarity before you start. Some late sixties Minis were equipped with dynamos but were still negative earth. Have a look at the top of the battery and see what terminal is connected where. (Negative earthed-negative earth!)
Disconnect any radios, electronic rev counters or any other electronic equipment.
Fit the alternator and bracket where the dynamo was. Tension fan belt.
Connect the heavy wire to the terminal marked ‘S’ or ‘+’
Connect the thin to the terminal marked ‘IND’ or ‘WL’
Locate the control box. Remove the black wire from terminal ‘E’, the brown/green wire from terminal ‘F’ and the brown/yellow or plain yellow wire from terminal D.
Connect these 3 wires together securely. Best to solder.
Remove the wires from terminal ‘AL’, ‘A’ and ‘D’ .Join them together too.
You should now have 2 groups of 3 wires soldered together.
Insulate the ends and secure them somewhere they cannot earth out. Insulate the terminals on the control box too.
Alternatively, if you want to keep some originality you can carry out this conversion inside the control box by removing everything inside and connecting the remaining terminals (as above) inside the box. This limits the chances of the wires earthing out too.”
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If you Mini is originally a Alternator equipped one then all I have said above has probably been a waste and thus my total apologies!
