We bought a VW New Beetle 99 for our daughters graduation. Nothing but problems after problems. Right now we are dealing with the airbag light on, and while driving the locks go up and down and the hazard lights go on.
We bout it for 3700, and have put atleast 2400 into after the fact. We have only had it since June, 2012.
It sounds like there is a grounding problem or a short somewhere.
If it is a convertible I would guess it might have water damage.
Attaached are wiring diagrams for the power door locks. Check the grounds and look for possible shorts.