Doesn't hurt a thing for your lights to dim somewhat. As long as you have a good battery and don't sit idling too long it's not a problem. I had a three pulley set on my 88 Mustang for years and never ran the battery down. I did use a lower ac fan setting in heavy traffic. You just have to watch your gauge and use common sense when in heavy traffic.Marine One:
You brought up an excellent point. On my 00 Vic (4.6 2V V8), the headlights did dim at idle and got worse when I had more accessories on at the time (HVAC blower, Air Conditioning, stereo, and turn signals).
I'm never going to try underdrives again in any vehicle, but that is just me. :SNSign:
For the extra 10 hp it may not be worth it for some. But for the true racer who doesn't want to be beat by a car lenth then they are definitely worth it. That's what they were worth on my 88, about .1 or a car lenth in the quarter mile. Might mention too save about 1/2 mpg with them as well.
On my 06 I don't notice any diming of the lights at night. My alternator needle never drops even with ac on high fan setting. I have the factory alternator pulley and idling at factory set speed.