Replaced alt. new one works fine but light stays on after I start driving seem to be worse the colder it is. When car is warm and restart light goes off fine

. Clean connections on the end of the "B" wire, which goes from the alternator to the mega fuse on the end of the under hood fuse box, with abrasive cloth. Apply dielectric grease.

. Check the regulated battery voltage, which should be 14 to 15 volts. If it's low, the voltage regulator/brush assembly may need replacing. This is a problem on many remanufactured alternators, where they are nice and shiny and look new, but they do not replace the old voltage regulator/brush assembly or bearings.

. Adjust the idle rpm to spec, if possible--it may be too low.