My GEN light came on this morning and my voltmeter dropped to about 10/11. I iddn't have my tester in my truck so I couldn't get an accurate reading. Throughout the day, there was no lag in starting, and every now and then, the voltmeter would read back to normal. When I got on the freeway to head home, (about 1 hr.) the meter came back up to normal and stayed until I shut it down in the driveway. I'm planning on changing out the Alternator and doing the external voltage regulator mod to be safe. Any other areas that I should be looking at as well?

 

Now it's been idling in the driveway for 10 mins. I haven't changed anything yet and theres no GEN light and it's charging @ 13.67 as read on my digital voltmeter.

 

I would check for loose connections first, but the brushes in the alt may be about worn out.

 

Made it 45 mins down the road on the way to work before the light came on. Now I've started it twice since and within about 3 mins. the GEN light comes on. This time I had my digital meter and when the voltmeter in the truck is reading a bit lower, it is 12.24. When the light is on, it is usually down to 12.24 but sometimes it will go back up to 13.67. I'm leaning towards voltage regulator based on this but I figure a alternator rebuild couldn't hurt.

 

If the tach. is not working properly as well it is the crank sensor. It tells the computer the engine is running and it sends power to the fields in the alt.. If the tach. is normal it's probably just a fully charged battery or the alt. is going bad. Mine had a bad crank sensor!!

 

A fully charged battery will not cause the alt light to come on-that would be like having the oil pressure light come on above 40 psi. The fact that his system voltage DROPS when the light comes on also precludes a fully charged battery. If the tach is working correctly, I would assume it's probably the alternator, or related wiring.

 

Tach is still working fine. I'll be picking up an alternator this afternoon so hopefully that's all it is.