I just heard from someone that having underdrive pulleys with a aftermarket sound system will cause your headlights to dim at idle.

Anyone experience this with F-150s?

 

this will probably happen, since your alternator will be spinning slower if you have a high powered system in your truck. How many amps does your current system pull? Give me the amp ratings on the fuses of your amps. If the headlights do dim with an underdrive pulley set, then you can combat this problem by putting a smaller pulley on your alternator, SLIGHTLY smaller is the key though.

 

You may have problems if you go with a pulley swap that has a larger alt. pulley. I did the ASP 2-piece pulley set (crank & water pump) and don't have any problems with my stereo system. I have a Kenwood CD player, Alpine signal processor that has a 10amp fuse, and Alpine 5-ch. amp with a 50amp fuse. Even with the heater on high and headlights on while the stereo is cranking I don't have any proplems with dimming lights.