Battery light comes on, shuts off, comes on shuts off
 

Any ideas? 2004 no mods, brand new batteries

whats it charging at?.

no clue i only have an idiot light

Time to buy a volt/ohm meter....they are cheap!

I have a meter what is the procedure to check please

I had the same problem this week on my '04 with 74K miles.

I hooked up a cig. lighter plug to a multi-meter and measured the voltage while driving. When working properly I saw voltage between 13.4 and 13.9, when the batt. light came on voltage would drop to 12.1.

The alternator diodes tested fine, but the unit was producing less than 30A output.

Replaced the alternator Wed. and have not seen the light since.

Have your alternator checked. Mine was doing the same thing a couple months back. I looked at my insight and found that it was charging between 9 and 11 volts at idle and below 2000RPM and as I ran it down the road the voltage would eventually go up to around 12.5 and the light would go out. I had brand new batteries and knew they were good so I stopped by Auto Zone and they confirmed bad alternator "free test".
Within 2 months of my alternator going out, I counted half a dozen posts on here for bad alternators with the same symptoms.

Check your battery cables for corrosion and tightness, check the water level if possible and add distilled water if they are low.
Meter to DCV Scale- Range to 20 (if your meter has that). Red meter lead to + post on either battery, black to -post same battery. Note meter reading. It Should be at least 12.25 (12.50 or more is better) if not, charge your batteries before you continue. Crank truck, stand around about 5 minutes and check again. If system is charging you should see between 13.somthing to 14.somthing maybe more.
If not at least 12.25 before starting truck get batteries load tested (Auto Zone or wherever) be sure they disconnect them from each other or a good battery may "cover up" for the bad one.
If not 13.? or better while running, could be Batteries or Alternator. If batteries pass load test pull alternator and have it tested. I prefer to get the origonal alternator repaired if there is a shop near you that does this. I've had better luck and also it's cheaper :)
Hope this helps.

Thank you!

Get your batteries load tested. My voltage was good but amps bad.
One battery had 625 cca & the other 635, it was 70 degrees out when tested.

Batteries were original from 04, had 92,000 miles on them when I replaced them a month ago.

Check your voltage on the battery posts and then also check on the terminals. See if there is a difference.
Sometimes you can get a clear type corrosion between the terminals & the battery posts at this time of year for some reason. I ran into it 2 years in a row on my jeep untill I started using a protectant.

Get a battery terminal cleaner, one side will have a round wire brush & the other a hole with wire bristles inside. After using the terminal cleaner, spray on some terminal protectant. It comes in an aerosol can & is usually red in color. I usually spray everything down before putting the terminals back on the battery posts.

Oreillys has a lifetime alternator for around 250. I personally have 2 of em. one on the truck and one in the truck. I travel in the truck for a living and was stuck for about 12 hours waiting on oreillys to open. so I bought 2 of em. if it ever goes out again I can just change it and replace the bad one when I get to another oreillys. I am sure the oreillys brand is kinda crappy n cheap,,,, but lifetime warranty, cant beat that. plus the fact that it only takes about 10 min to change it. just my .02

my 04 doing the same thing replaced alternator still battery light came on had batteries and new alternator tested all tested good cleaned battery posts and cable ends to no avail any other idea would be appreciated

Get your transmission checked. If all other parts are new and it is still acting up that mean there could be a malfunction somewhere in your transmission. Check the fluid in it first. I read on another forum of this when mine was acting up. Turned out to just be loose alternator wiring with me but that could be it for you.