I have a 2008 Honda rancher 420 es. It will not down shift electrically. But it will upshift electrically what’s going on??

Downshift button dirt/debris so no good contact in switch, fuse/relay bad or shift fork /gear dog problems have you tested with a test light? Also try to install the backup shifter from the toolkit and see if you can get it to work this way... assuming you haven’t already tried any of this??

best of luck but normally a dirty contact... contact circuit board cleaner is best or use carb&choke cleaner, pine sol and stiff tooth brush/ or preferably a soft metal brush to scrub with any of these chemicals. Or a small screwdriver to score and clean the metal contacts the best you can with screwdrivers... also citrol a citric acid cleaning solution made from Schafer’s they make great products (not extremely cheap.) but the us military had it possibly still does contract them for their oils, cleaners and other chemicals... regardless their products have not once let me down... it fixed my wr450f blinker problem from within the switch [dirty contacts]