03 6.6 with Charging Problem

[TowmanTug]

Hey everybody!

I have a 2003 GMC 5500 with the 6.6 The voltage gauga started showing 12 volts last week. Its usually right on 14. I tested it at the batteries with engine running and I get 11.7 to 12.0

This truck has the dual alternators. I pulled them off and had them bench tested. I was told one was bad, one was good. I replaced the bad one and it still charges at 12. I puled them both off again, went back for bench test and they both work on the bench. Even testing for voltage at the back of the alternators I get the same reading I was getting at the batteries.

Anybody been thru this? Any ideas? Before somebody says batteries, I replaced those before I ever touched the alternators. I figured the batteries may be going bad since they were original.

Thanks!!

[Mark Rinker]

Bad cable somewhere - i.e corroded and green internally under the insulation?

Check all grounds.

[leolkfrm]

Had a similiar problem. I have single, lost voltage, light was on. Ok low voltage at battery so its bad. New(rebuilt napa) one showed voltage on dash and on meter at batteries, light not turning off. Did like you asked forums and searched finally took it off exchanged it and all is fine. I do see a delay in the voltage kicking in at start-up but all is good! good luck

[DmaxMaverick]

The "voltage delay" at startup is normal. The glow plugs and intake heater (if it's cold enough) draws a lot of current. When you see the meter jump up a few seconds after startup, that's the GP/heater turning off.