Here's another post on it. Sorry I can't give any great info myself, since I don't have the armor. As far as the second piece, as long as nothing metal is shorting it, you should be good however you attach it. I designed it to fit under the other side of the chest, so that it would be somewhat balanced (vs having an entire circuit under one side, and nothing on the other). But since it isn't visible, anywhere it'll reach and not get shorted should be fine.
I made a 1" wide "U"-shaped piece out of 2mm Sintra that goes over the light board and is GOOPed on each end to the inside of the left breastplate. The "U" piece has little tabs on the ends that are the parts that are actually GOOPed. The secondary board and 9V fit inside my left chest pocket.
I made two 4 sided boxes out of thicker sintra and superglue, then put a back cover on it with thin sintra. The boxes were made to fit the 2 boards perfectly. I just use clear shipping tape to hold the two boxes to the back side of the armor, the tape is very strong and super easy to remove. This works like a charm, doesn't take very long, and adds protection to the light board which is good cause they sure ain't cheap. I made cut-outs in the vest to make the armor sit flush and hide the wire band. I 've been meaning to sew in a tiny piece of velcro into the vest to hold the battery securely too. I'll just slap a tiny piece of the sticky backed velcro to the battery itself.
Ok, I cut two square holes in the vest on either side of the chest armor, and glued the lights into one side and velcro'ed the secondery board into the other side. A friend of mine that is good with electronics got it to work agian after a bar of magnets I am using to attach my armor into place shorted out something on the secondary board. I have the battery in a thrid cutout inside the ab plate.
that is a great job, I ended up epoxying it in with a sintra shim then covering it with electric tape. I have the secondary board velcroed in and the battery is on the side of the vest, a small push button switch is right at the underarm.