I often paint very small details like knobs, switches, and wiring with a toothpick. It makes a very small brush. I shake a bottle of paint, remove the cap and set the cap down upside down on benchtop. A thin film of paint will stick to the liner of the top. I then take a toothpick and stick one of the points down into that film- A tiny drop will stick to the end. I then daub it on the detail area I am trying to paint and a small spot goes onto the detail. I then repeat as needed. You can draw the toothpick along like a brush, but not very far, because of the limited amount on the tip, so you have to dip the pick into the cap/lid far more often than with normal brush painting but you can get the tiniest spots and thin lines of paint on raised detail with this method.
I use those double ended toothpicks with the very sharpest tips.