Rant: stop telling new techs to buy a $400 scan tool first
I have watched three kids in a row at our shop in Boise sink their whole first paycheck into a fancy scanner when a $30 test light and a wiring diagram would have found the bad ground in 20 minutes, so can we please start teaching diagnosis before gadgets?
Skip the scanner money and grab a power probe and a good meter instead. Spent years chasing gremlins with just a test light and learned more than any fancy tool taught me. Make the new guys trace every circuit by hand for a month, then hand them the gadgets.