I've tried every paint, ink and fabric pant known to man. Most of them do not work or only work on certain fabrics.
For the circuit board I used a gold metallic spray paint. For the grey symbols and letters I used silver metallic spray paint and then sprayed over that with a grey spray-on fabric paint.
I spray the back of the stencils with a low-tack spray adhesive so they stick to the fabric. Be careful though, depending on the fabric the stencils may leave behind sticky residue.
This little stencil project has been a nightmare. I've spent way too much money on fabric paints, wasted a lot of time and ruined several articles of clothing and just generally made a huge mess.