Battery in Trunk wiring completed, now no power at all

The Wipers get their power from the ignition switch and so does about 1/2 of the fuse box.............................So the ignition switch is working.As is the the ground path from the wipers to the battery.
The headlights and horn do not go thru the IgSw., The headlights also do not go thru the fusebox, but the horns do.If the wipers have a ground then so should the horns, So I bet the horns are not getting power.If the wipers are finding a ground then so too should the headlights, as long as you remembered to secure the little ring terminal behind the LH headlight to the core-support. That sorta leads me to think the headlights are also not receiving power.
So now we go back to the location where the starter-relay was originally installed. IDK what car we are working on so I'm flying by the seat if my pants here, But there should be one or two wires small gauge wires connected to the big stud. Those are power take offs for the ignition sw and headlights. Are yours connected? If yes then follow them up to the bulkhead connector. Here they should terminate with fusible links. You will have to make sure power is there and getting thru. And not just enough power to work your multimeter but serious power, so a little tugging is in order. If the power is there then it goes thru the bulkhead. One wire then goes to the ammeter and then the ignition sw, and the other wire goes to the fuse box. There are about 3 fuses in that box(A-body) that are always live, the brake sw, the horn, and the hazzards. See if you have power there. The ignition sw powers up all the others. That should keep you busy for a few hours.