If I am not planning on an electrical system, can I reuse my camper van’s original ceiling and mood lights In my build without killing my vans battery
You can reuse the ceiling and mood lights, but the real question is how they’re powered and switched. If they currently run off the van’s starter battery with no isolation, leaving them on will drain it. A simple approach is a small separate leisure battery or a low-voltage cutoff, so the lights can’t pull the starter battery flat. Also check the current draw of the mood lights, since older incandescent ones add up quickly. LED replacements help there. How are they switched now?