the high beam post reminded me of this, i have the ultra lite bulbs in my truck and they work great on high, but the low beams will work for a short time "normally" then after say 10 minutes whether its low beams or daytime runners, the lights have like a pulsating flicker to them it really annoying and other drivers think im flashing at them. my volts are fine on the alternator andeverything else electronic works fine...any ideas? and its both lights btw

 

i was out today playing with it, i was told it could be bad ground somewhere, im mechanically inclined but the whole electrical thing isntthe sharpest part of my knowledge

 

When this happens pull off the road and...
...leave the lights on but turn off the ignition. Do they still flicker? If no, alternator problem (maybe in the voltage regulator). How's your belt tension?
WC

 

...i dont know if it would be a goound since you sau it only duz it on low beam not high beam, and they use the same ground, put your other bulbs back in and see if it duz it, if not its mostlikey in the bulbs themselfs when the heat up