I have a lawn chief with briggs and stratton 12hp. I had a problem when the battery pos terminal melted off the battery. How? Have no idea, I think it bounced up and shorted out under the seat. Anyway,
I replaced the starter switch, silenoid, and battery. I still get no power to the key switch.
There is juice from the battery to the silenoid, but nothing to the key switch.
No headlamps and even the voltage gauge doesn't even move.

Have you checked your fuse?

Yep, it's the little things that get you. Mowerman is likely correct.

Chunky:

Your post doesn't tell us that you replaced the battery. Let's ( u me) that you did. The "FUSE" is likely not a fuse, but a fusible link. A short piece of wire with a dramatic diference in size in a good location.

I've not seen very many if any that I recall fuseable links between the key switch and the solenoid. Could be wrong here. But I believe he will find a red wire with an inline fuse holder.