Tail lights blinking
 

Hello FORD enthusiasts, question that's beyond my pay grade... 2011 F-150 crew cab 4x4, problem started when truck wouldn't start like a dead battery. Jumped and immediately started no problem, drove a half hour and stopped at store, started fine and all good. Parked at house and friends stopped over and reported truck tail lights / brake lights were flashing. Fellow mechanic recommended unplugging trailer plug receptacle behind bumper and waited but same thing, lights blink every couple seconds. Who's the electrical gremlin slayer champion ??? Any ides or cures for known issues of this nature ? Thanks Drew

It will do that if the battery voltage drops to the cutoff for the electrical system. I believe it's somewhere around 9V. Anyways, it sounds like you may have a bad battery, a bad alternator, or both. One can cause the other.

To test, place a voltmeter across the battery terminals themselves with the engine off. Then check at the copper wire itself at the crimp. These should be the same; if the terminal to terminal is higher, you have a bad termination. What voltage are you getting?

Crank it up. What does your voltage read?