I have a 2011 f150 5.0 XLT that I just replaced a alternator in. Once I replaced it and started the truck I noticed the battery light came on and the lights were pulsing and the engine sounded like it could die at any second. The battery was running at 14 volts and I brung it to the shop today and they said the alternator and the battery is good. What could be causing the engine to sound like its about to die and the pulsing lights?

 

I had an '11 standard cab with the V6 (3.8 I think, can't remember) that acted like that. Got a wrench icon on the dash display but no engine codes.

Turned out to be the wiring harness on the transmission. The wire tie broke, it dropped onto the exhaust, which melted the insulation and it shorted out. Lights flickered, ran rough and shifted hard. Other than that it didn't damage anything. It's a $700 repair at the dealer (the harness is $136).

It's on the passenger side. Take a look and see if maybe you're having the same issue.

 

Sounds like the voltage regulator in the alt.. re-man Alts are hit and miss.