Dimming lights

Hey guys, I had my battery checked by a sears underload and the battery gauge went to 12volts and the lights dimmed. The attendant said that it was within spec but my gauge a while back used to stay at 14volts and no dimming of the lights.Any ideas what to check it is 98 SILVERADO K1500 5.7 also the alternator has never been changed since I had the truck for 10years and the belt is tight. Thanks

Sounds like the voltage regulator (inside the alternator) Is getting ready to pack it in.I have a small alternator shop fix mine but most just put in a rebuilt one.
Good luck!

Hey guys, I had my battery checked by a sears underload and the battery gauge went to 12volts and the lights dimmed. The attendant said that it was within spec but my gauge a while back used to stay at 14volts and no dimming of the lights.Any ideas what to check it is 98 SILVERADO K1500 5.7 also the alternator has never been changed since I had the truck for 10years and the belt is tight. Thanks

since the battery was load tested as good , I agree that you are in need of a new alternator...the alternator output is not solid 14volts but a chopped waveform which is lacking full power...soon the output will fail totally...


It is possible to measure the current output of the alternator...as on my vehicle with all devices on the current produced is 66 amperes...this testing though , is hard to find.... as many repair shops lack the technical skills to perform this test....

the other item to check is the connections to the field at the alternator .this small wire excites the field and this then creates your output.. I have seen on older vehicles corroded wires here...also the fuseable link within the alternator output wire the large wire , have resistance/corroded ...


when you replace the alt. make sure you disconnect the ground connection to the battery first...

Thanks for the reply guys, looks like I will get another alternator soon.