You can find the drain by sequentially removing each fuse and checking for a current draw on that circuit. Only the clock and alarm should draw any power.
It would help to know "what" every-so-days means. 2 days? 2 weeks?
As mentioned earlier the alarm does drain the battery and the manual even spells out that if you are storing or rarely drive the car to disconnect the battery.
If it is every 2-3 days then I would disconnect the alternator battery wire and see if the problem goes away.
I own a similar version (1990, 4.0 L) and this has started happening to me in the autumn.
It appears that the battery is too flat to spin the motor after three days of non-use. The temperatures have always been above freezing. The battery is about five years old.
I removed the fuses to the alarm after the second drain to remove it from the equation.
There have been no other electrical problems, whatsoever.
It's too cold here (about -43 degrees, celcius, with the wind chill) to play in the garage, so I haven't started removing fuses yet, but I'd be interested in the experience and ammeter readings others have found.
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