'87 Sami SJ  stock no mods
I've read everything I can find on this and other forums referencing beeping under dash and mine seems to be a new beep. There is a constant beeping from under the dash, my ears are shot my wife says it comes from near the center.
The only time it stops is if you turn on the lights- park or headlights.
It makes no difference if the keys on or not in the ignition, clutch in or out, doors open or shut, seatbelts fastned or not, sitting in the driveway or going down the road. The reset switch under the dash makes no difference.
Please help before I run my battery down from leaving my lights on.
Ed

Stick your head under the dash and follow the noise to the beeper and unplug it.

I'm not certain if the Samurai's were fitted with them, and it may vary from one country to another, but my '93 Swift has a beeper under the dash, near the center, on the passenger side.  It beeps if the driver's door is opened with the key in, engine off, or if the door is opened, lights on, key in, engine off - I'm guessing you have a wiring problem that may be causing yours to beep when it shouldn't.