From the frequently asked questions off of Tekonsha web page:
Q. The top or bottom horizontal bars are flashing.
A. If the top bars are flashing, this tells you that the control is mounted at too steep of an angle. If the bottom bars are flashing, this tells you that the control is mounted at too low of an angle.
You didn't say what was flashing, and I don't have one. May need to check their web page and look for a manual. Good Luck.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT