Hi All,

A while back, while towing a small U-Haul trailer, i noticed that the battery light was flickering. After i unhitched, it went away. Recently, I added several hundred pounds of weight to the bed in preparation for the snow and ice, and the light came back.
After i start the truck, the light is steady. Once the engine RPMs are up, the light goes off, but comes back on again as soon as the RPMs return to idle. After 5-10 minutes, the light flickers for a while, and then goes off completely.
So basically- charging system issue while at idle, but only for the first few minutes after starting up.
I have tested the battery with the engine off, with the engine running, and with the engine running while there is a load (headlights, etc.) and everything checks out fine. The alternator is new, as is the serpentine belt. I just cleaned the battery posts and replaced the terminals.
Anyone have any other thoughts on what could be causing the light to come on despite no obvious actual electrical issue??

Thanks in advance!
Brett

 

how did you "test" the battery? that's what it sounds like to me. If you are just checking for 12v that may not be a good enough test, you could take it to advance auto or someplace to have them run a test on it for reals. Or just try a different battery and see if that fixes it.

And I don't know if it might be possible, but could the previous owner have put in the wrong battery thats not meant to meet the rangers requirements?

 

I just did a simple test with a DMM. AutoZone will probably be my next stop.

I'm the original owner, so I know the battery is the proper one.

 

You can do some basic tests of the charging system as follows:

Start by pulling the battery, fully charging it, then having it properly load tested. Some Auto parts stores can do this. Once you eliminate the battery as a possible cause look at the charging system and associated cables.

If you're handy with a voltmeter you can do some basic test to help identify potential problems with the charging system.

Note: all tests should be conducted with a fully charged battery and after ensuring all fuses are good. Don't Assume they are...Test all of them including those in the Power Distribution Box under hood.

1. On Vehicle Test – No Load Test
Connect the voltmeter’s positive lead to the B+ terminal on the alternator and the negative lead to ground.

Ensure all electrical accessories are turned off.

Start the engine and maintain 2000 rpm, check the voltage reading. It should read between 13.0 & 14.5 volts.

2. On Vehicle Test – Load Test
Connect the voltmeter’s positive lead to the B+ terminal of the alternator and the negative lead to ground.

Start the engine, check the voltage reading and write it down. This is your base voltage. Next turn the A/C on, the blower motor on high speed, and the headlamps on high beam.
Increase the engine speed to 2000 rpm. The voltage should increase at a minimum by 0.5 volts above the base voltage.

If the voltage increases as specified the charging system can reasonably assumed to be operating normally (Per Ford Service Manual).

3. On Vehicle Battery Cables/Connections Test

Positive circuit test – Connect the voltmeter’s positive lead to the B+ terminal of the alternator and the negative lead to battery positive terminal.

Start the engine and maintain 1500 rpm, check the voltage reading. It should not exceed 0.5 volts.

Negative circuit test – Connect the voltmeter’s negative lead to the alternator housing and the positive lead to the negative terminal of the battery.

Start the engine and maintain 1500 rpm, check the voltage reading. It should not exceed 0.5 volts.

If either test exceeds .5 volts look for signs of a bad connection between the two points, i.e., corroded battery terminals, cables, ground connections, etc.

If these test do not identify your problem, I'd recommend having knowledgeable mechanic check the system.