412 Electrical Problem

[lansdownplace]

My 412 electrics are being temperamental. It has a new alternator, regulator and battery and charges nicely at 13.5v. and then it just drops at random to 11 volts or so. Turning systems like the stereo, lights or heater on or off makes no difference and doesn't trigger or solve the problem. The fault seems to be intermittent but has already claimed two alternators, a regulator and a battery it seems to be pretty destructive. How would you tackle it?

regards

Paul