I was driving my 350 2006 6.0 after it sat a day. It had trouble starting as if the battery was low but ran fine after getting going. I had been freeway driving at night with the headlights, road lamps, fan and radio going for about 30 minutes. I then noticed that the dash lights and radio lights were flickering ever so slightly. After another 10 minutes the service lamp came on. After another 5 minutes the radio stopped working and the engine started hesitating. I shut off as many electrical loads as I could and I made it home. I had a similar problem in my 96 Bronco where a main fuse from the alternator was dislodged and the vehicle just ran on battery till it died. I checked all of my fuses and relays and all seems to be in order. It's late at night and I haven't been able to do a good check on the alternator. I'm charging the batteries now, but I'd like some advice on things to check to see what the issue is. Any advice?

 

Did your batt light come ?

 

A cheap thing to try is replacing the brushes in the alternator. I think this is possible with your alternator. Usually the rotating assemblies are just fine, the problem is the brushes wear out or the voltage regulator is fried.

Also, check your connection to the alternator and your battery connections. Make sure they are nice and clean. The issues you describe can also be cause by a bad ground.

Here is a shot of the brushes when I replaced them in my Ranger alternator.

 

I'd pull the alternator and take it to a parts store that can test it.

 

maybe first test it on the truck and see if when it's running you get 13+ volts at the fuses [you may want to make the engine run a bit higher than idle to make sure the alternator could be putting out enough juice].

If you don't get that, then I would remove it and bring it in for testing.

 

Before skipping right into major component failure lets start you off with some basic troubleshooting 101:
Troubleshooting is a road map to follow, beginning with the simple items then on to the complex. Dont throw parts at it. Lets find the problem first...

In a negative ground system, grounds are your friend...all of them. Sounds to me like a bad or loose connection. Especially at 9 years old.

Does the truck crank and start ok hot and cold?

Hows the serpentine belt?

How many miles on it.

What service has been recently preformed if any?

Follow these steps:

1. Check for loose or bad connections at the alternator, both the batteries, starter solenoid, the starter and both ends of all the battery cables. Verify all is clean and tight, even the lighter 8-10 gauge wires attached to the inner fenders and core support fire wall etc. Is there a ground strap going from the engine to the firewall? Should be and it too needs the treatment. Remove and ohm test each of the secondary (battery) cables. They should have very low resistance and be in good serviceable condition. Replace as needed. Problem go away? If not proceed...Now that we have the cables and corresponding connections out of the way...move to step 2.

2. Dead load test the batteries with a good load tester. Pass or fail? Fail...replace battery.

3. Run truck and probe both batteries positive terminals to a good ground with a volt meter. Same voltage on both batteries? Is it 13.8-14.2 at idle? Different voltage indicates a bad connection, battery or cable. Low voltage can be a bad connection or a bad alternator.

4. Tap the alternator with a 2x4 or dead blow while its running. Does the alternator wake up? This indicates that the brushes are stuck in the rig or worn out. Or the commutator is bad. Either way have it bench tested and rebuilt if it fails.

So replacing the alternator moved to the bottom of the list. It could be just a bad connection saving you $100s and hair.

Close the loop here when you find the problem.

 

Only the service light came on (orange wrench). No battery icon ever came on.

 

Thanks guys. I'll be pulling the alternator to test it. I tried using a multi-meter at the 12V outlet in the dash and only got about 12.3 while the vehicle was running (even with high idle). Alternator is very suspect.

 

Before you replace the alternator, most of what I said still needs to be checked and performed such as battery condition, cable condition and good grounds. Otherwise you will over tax a new alternator because its still compensating for other "weak" areas. And the other weak areas could be what contributed to the alternators demise in the first place.