Can anyone give me some pointers to sort out the following electrics problem with my UK '98 740 (D24T)?

When ignition is switched on only the Glowplug, Oil, Parking brake and Safety Belt lights come on full strength. ABS light comes on and then goes off.

Remaining lights - Battery, Bulb Sensor, Washers etc are showing only a very faint glow (maybe Battery is slightly brighter than the others).

Engine starts fine and ABS light comes on/goes off immediately (ABS is working OK). Battery light etc remain glowing, but not brightly.

Voltage across battery with engine running is only around 12v.

So I'm assuming 'no charge'.

This problem occurred intermittently a month ago and the garage diagnosed failed Alternator, so it was replaced. Battery also replaced. Everything has been fine up to today when the above problem re-occurred.

The only other snippet of information I can give is that with the ignition on, and the red wire that goes to the D+ terminal at the Alternator disconnected it is showing 7.5v - which seems strange to me, I'd expect 12v.

Does it look as though I've got another blown Alternator or could it be some bad earth somewhere. Is it possible to check the actual output of the Alternator ( I have got a digital AVO meter, but not much experience in electrics!)