Any advice would be great! I recently noticed in my 89 L6 4.9L truck, that the battery light was coming on and off. My charging guage showed it was OK, and I tested the battery which was fine. The past few days, the starter motor wasn't engaging after the first couple of turns of the key, then it would engage and start. After starting, I've noticed it's been running rougher until warmed up. Yesterday, the starter motor engaged after the third try, it ran for a few seconds, then died on me. Now it cranks but wont start.
I replaced the altinator last year, the fuel filter last week. I checked the Battery again and it's ok. The serpentine belt is good and not slipping.

Any ideas where to start would help. I think it's electrical problem and was planning on replacing the starter, however, since the starter is engaging, I'm not sure where the problem might be. The truck has always started right away in the past.

 

The battery light comes on when the demand from the electrical system exceeds the output from the alternator. You should check the alternators output. You keep saying the battery is good. How are you determining this? You also need to find out if you have spark and fuel when trying to start it, but I'd concentrate on the battery for now.

 

I checked the battery with a battery tester. I'll start with the basics fuel/spark also, but will look at the electrical close. Thanks.

 

I wasn't trying to be rude, I wanted to find out how you tested the battery. If you have a voltmeter, you can test the battery and the alternator output, and see if the alternator can handle loads like the high beams, etc. It's possible that the alternator is working, but not enough to handle the loads you might have. If you have extra lighting, and an expensive stereo, or entertainment system, that could be part of the problem, too.