GEN/alternator light is on

Inserted my xj's battery today and started her then noticed that the GEN light on the instrument panel is on. I started her last weekend and the light was not on. What could it be?:eyes::eyes: She is charging just below the halfway mark. Could somebody help out please.
Steve

put a meter on it. Do not just trust the factory gauge. The alternator could be bad even if it is showing that it is charging, i.e. it could have a bad diode in it(stopping the small amount of a/c voltage(bad for a battery), that all alts make, from getting to the battery). The battery could have a bad cell in it, could be bad wiring in between (badly corroded), etc. Not sure what you are near but if you are near a parts store or shop that could test the alternator I would get it tested.

thx for the advise. will remove it and take it in to be tested. here in South Africa you have to take the darn thing out to have it tested. we are not so far advanced as you people yet. maybe in 50 yrs time.

Set your multimeter on volts. Check battery with engine off. Shoulod be close to 12.5. Start engine, check again. Should be 14-14.5. If it doesn't go up, alternator isn't charging. As usual, make sure all connections and grounds related to the battery are clean and secure. Battery terminals and grounds. You need the complete 360 degree circuit. Take apart, clean with sandpaper or scotchbrite, clean debris with starter fluid, brake cleaner, etc., and reassemble. This fixes at least half of the problems.

had a look today that the alt light goes off as i start the motor. then as the revs settle the light comes on again. this thing is giving me a headache. the alt is charging at 13.8 avg and when i put the spots on the dash gauge hardly drops. any suggestions????