Bongo Fury

OK dear forum members - I'm facing confusion, or being supremely thick.......would not be the first time.

When I got my bongo, 3 years ago, I installed a leisure battery, split charge solenoid etc, including a new under bonnet fuse box to run ancillaries from the leisure battery as required. The mod included wiring the stereo constant live to the leisure battery, and also the cabin interior at fuse point 1, and other interior loads at fuse point 8. It has worked perfectly for two and a half years, then the fuel filter light and alternator light began to glow dimly. A new fuel filter was fitted and water trap drained to no avail (in my heart of hearts I knew it wouldn't help). Various calls resulted in the conclusion that the alternator was failing, and indeed it struggled to output anything above 11volts. So new alternator fitted and all seemed well for 12 weeks, until I noticed that the headlights got bright on acceleration, and dimmed when accelerator was released; 2 days later I had a flat battery, well actually a completely dead battery verified by 24 hour charge (on garage charger) but seemingly dead cells. So I have fitted a new starting battery, checked alternator out put and all seems fine, except that:
Lights still get bright on acceleration and I noticed a significant spark when I connected the +ve starting battery terminal; the multimeter indicates that something is drawing about 1.5 amps - which stops when I remove the fuse at position 1 (cabin).
I have checked all the interior wiring (except the remote locking system which is in the drivers door). I have completely isolated the leisure battery (+ve and -ve) as well as disconnecting the radio.
I have not tried driving with everything isolated at night (to see if the lights dim) but thats next.
Anyone have experience of any of this?

Not sure if its correct but the center light is known to draw amps when the bulb is failing even when off for some strange reason so it may be worth removing the bulb and testing, new bulb from electrics shop about 2-3 pounds

I also found the radio drew too many amps and I had to put an inline switch for the permenent live to stop it flatening the battery.

probably neither but worth checking

Do you have a multi meter to check the voltage of the S/B with engine OFF (12 - 13 volts), engine idling (12.5 - 14volts) and engine at typical revs (13.5 - 14.5 volts) for driving ?

If you've got a cd multichanger fitted they draw over an amp for about 20 seconds during their start up procedure - that's every time you disconnect the battery.................

Thanks all:
Voltages on S/B are correct and as described.
No CD changer fitted - just single CD/Radio - but the draw seems to be continuous.