I was rooting around in our storage shed and found a Ray Jefferson L-400 and
I don't recall where I got it from.

The L-400 isn't one of the common ones by Ray Jeffereson. The L-100 and
PL-99 are much better known. The L-400 has 200 waypoint storage capability.

This thing has the owner manual with it, and I've reviewed it thoroughly.
One problem is still there, and I need help with it to get this thing
working.

The set does come on like it should, and automatically finds our GRI, etc.

The part that's weird is the keypad area. There are two distinct groupings
of the touch keys.

One groups is (In addition to being numeric):

L/L, WPT, TDs, TTG/COG

The other group is (in addition to being numeric):

L/L, WPT, TDs, STATUS

The remaining keys are (in addition to being numeric):

HOME, FUNC, SAVE, CHANGE, ROUTE, PREV, NEXT

I need some help figuring out what the two grouped sections are functionally
for.

At first, I thought it might be that one group handled waypoint #s 01-99,
and the second dealt with waypoint #s 100-199. However, there are
functional differences between the upper and lower key pad groups. So, I
now doubt that the split waypoint sections are the reason for the
difference.