• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Alternator not changing battery?

BrokenXJ

NAXJA Forum User
Location
Massachusetts
OK, we are 1/2 mile into a snow run when old Broken dies because there is no power to run the fuel pump. The alternator light didn't come on, but other people on the run were convinced it was the alternater. So out comes the new alternater(spare) and we change it in the snow. Did not help, so we charged the battery for about 1/2 hour, and made a mad dash back to the tow rig.

Now I'm really confused about this electrical system? If anybody has any ideas, I'd be glad to hear them. I have a volt meter, to test connections but don't really know where to start?

BTW: 88' XJ 4 Liter
 
Start by testing battery voltage between the two terminals with the engine NOT running. Should be about 12.6 volts, I believe.

Then start the engine, let it run for a minute or so, and test the battery across the terminals again, with the engine running. If the alternator is producing charging current, it should read 13.8 volts.

If it reads 13.8 volts, leave the engine idline and turn on the headlights, then test again. If it's still not up around 13-1/2 volts, the alternator can't handle the load of the lights.
 
Back
Top