Battery light came on

My battery light came on and it's staying on for the last couple of days. The clock is also not lighting up. Any idea what this could be... bad alternator? Truck is starting and driving just fine otherwise for the most part. battery is only 2 years old. attached obd scanner stats in the comments below.

 

^Check battery charging voltage with the engine running and go from there. Could be bad alternator or rotted wiring (either power or ground). Is your alternator original i.e. 27 years old?

 

this is from my obd while running

 

Always start with good bright metal contacts on all connectors and grounds.

 

Check with a real multimeter between battery terminals; between the alternator output stud and casing; and between the alternator case and battery negative. On a newer vehicle I'd just swing an alternator at it. With a '98, rotted wiring needs to be ruled out first.

 

super clean truck, not a shitbox. don’t think any of the wiring would be rotted. i don’t have a way to check the voltage unfortunately, might go by the tool… but what am i looking for once i test it?

 

^It's still 27 year-old wiring. Something as simple as spilled oil can accelerate the deterioration.

> between battery terminals;
Check this to confirm actual charging voltage. If the clock is no longer showing, your actual condition is likely worse than the OBD2 reading suggests.

> between the alternator output stud and casing
If this reads similarly low voltage as at the battery, the alternator is likely bad.

> between the alternator output stud and battery negative
This should read similarly low voltage as at the battery. Higher voltage there indicates bad charging wire.

> between the alternator case and battery negative
This should read close to 0V. Any voltage there indicates a bad ground.

Keep the battery topped up with a tender and avoid trips longer than 15 minutes or so until you get this fixed. Otherwise the engine can quit any time and strand you.

 

ok, thank you!