How do I write a configure.ac file to default sysconfdir to /etc?

[Jim Lynch]

I have an application where most of what I need installed goes to
/usr/local/*, except I really want to put stuff in /etc.  By default
sysconfdir gets set to /usr/local/etc but if I do a ./configure
--sysconfdir=/etc I get what I want.  However as I advance in age, I
forget more than I used to so remembering to add that parameter
especially after a couple of months being away from this application,
I'm trying to put something in configure.ac.  I've found the sysconfdir
variable documented and thought something like this might work:

    sysconfdir = /etc
    AC_INIT(dummy.cc)
    AM_CONFIG_HEADER(config.h)
    AM_INIT_AUTOMAKE(panelprobe,0.0.4)

But no, it didn't.  Can someone tell me the proper way to default
sysconfdir to /etc?  I've googled a bunch but haven't found exactly what
I'm looking for yet.  I'm probably missing the correct search terms.

Thanks,
Jim