My dads truck shutoff while driving the other day after the battery light came on. He restarted and hasn't had any running issues since.

I plugged in the SGII and the main ficm power was right at 48, his other ficm voltages were at 15. I then checked the voltage and it read 15.5. We popped the hood and alternator said it was putting out 15.5 volts. We then check both batteries and they checked out low so we replaced them. The battery light is still on and will go in and out intermittently.

Any thoughts?

 

The voltage regulator is causing the alternator to over charge. Unless you can find a place that rebuilds alternators, you'll have to replace it. Running it at that high a voltage will boil out your new batteries pretty quickly.

 

If you checked the alt. output with a trusted multimeter than it's time for a new one. 15.5 will nuke your batts.

 

You should also clean Both the main engine grounds that may help.

But if you clean the grounds and it still putting out 15+ volts I wouldnt run it anymore be a shame to waist them new batterys

Check into a DC Power alternator they are good units if you can spend that kinda cash on it. The chain part stores are hit and miss on Good units

https://www.dcpowerinc.com/

 

Thanks for the insight. I assumed that the voltage regulator was internal but I have never seen an overcharge issue.

Would the alt. still fail the typical test at the parts house?