Here's what I think I know about that (from unpleasant experience):
"Upstream", if you will, is DC power & pickup coil.
That stuff can produce various symptoms, but not outright failure of the CDI.
"Downstream" would be primary wiring, HT coils, plug wires, & plugs.
There's some thought that problems here could induce failure, but other sympoms would show up first, or at least in connection with the failure.
There are usually common sense tests that can be made to isolate where the problem is and isn't.
The factory knows there is a problem here and has been pretty good about extending goodwill replacements, although they require something beyond shade tree diagnostics.
The igniters come in those packages that say "must be installed by trained service personell".
My first replacement came under warranty, and was installed by a "trained tech".
The unit is supposed to be secured by two sets of two piece ribbed shank rivets.
You squeeze 'em together to snug 'em up.
The trained thechnician who did the work used one rivet & didn't tighten it.
In lieu of the second rivet, he used a bolt & acorn nut that kinda fit.
I always wondered if that contributed to premature failure of the 2nd unit.
This is the same guy who insisted I bring the bike back to him for his diagnostics when it failed the 2nd time.
That didn't happen.
