In alt.home.repair, on Tue, 19 Dec 2017 10:35:17 -0000 (UTC), "Danny D."
wrote:

Normally the Generac generator feeds the whole house.
No fuse is tripped and I switched them all anyway (like everyone does).
What would make a generator only feed half the house? (if that)

At first it wouldn't go on automatically -

Didn't it come with an instruction manual that deals with this, at least
a tiny bit?

so that may be a clue.
I had to switch it to automatic from manual and after a dozen of those
switches, it went on automatically.

I'm wondering how to debug the transfer switch but I opened both up and
they seem to be the same with no moving parts.

Any ideas?

Like trader says, use a voltmeter. When you find the bad part, google
the part number and you may be able to find the exact replacement by the
same maker. If not, you still may be able to find the part online by its
name..

But if not, Generac might/should have it. Make sure the generator
isn't going to start when you're replacing the part.

A short story, my friend had an oven that was broken, maybe it was just
the light that didn't go on, and I got her to call my friend, who is an
electrician. He told her she needed some part or assembly and that he
couldn't get it, and he didn't charge her. She took the thing apart and
found the actual switch inside the assembly and bought it online for
much less money, because it wasn't the whole assembly. I don't know how
common such a situation is.