Generator/ alternator Light glows dim
 

Ok my alternator light glows dim all the time. I had the alternator rebuilt a while back and I have only driven the car about 100 miles since. The battery at idle if I check with a volt meter reads about 12.9 volts and if I rev it up it will go to about 14.2 but the light never goes completly out. I read some things leading to bad grounds. Is this possible?? I did notice the wiring harness for the guages looks like someone redid a lot of it (all the same color) And did not do the best job. Any other possibiltys??

Ben

External or internal voltage regulator? Was a resistor added across the generator (alternator) light? Jim

External Reg and No resister that I saw!. Sorry I did not mention that it is a marchel alt. I also bought a new regulater and it did the same thing

Ben

Slipping belt.

No checked several times. Its perfect

Ben

Ok, then oxidation on the terminals.

You don't say what year your car is (perhaps include in your signature line) but there should be a 14-pin connector on the engine wire harness that connects to the electrical console. Pin #11 of this is connected to the "blue wire" excitation circuit- make sure it is clean. You can clean it with denatured alcohol and an ink eraser, emery cloth, or electrical contact cleaner. If you take apart the headshell for the connector make SURE you have the wiring diagram handy because the wires WILL pop out of their slots, leaving you to figure out which goes where. Also, one of the wires from the harness is a brown ground wire that's just as important to proper functioning as the other wires.

Check also for oxidation around the terminals on the alternator, and where the fat red wire from the alt connects to the starter. Chances are you have a high-resistance connection there somewhere, which is being overcome when the alternator puts out greater current at higher revolutions. The problem is, every time it revs up, it heats those high-resistance connections, making the problem worse.

As far as the wiring harness goes, I recommend you get the appropriate wiring diagram for your year car and rebuild it with the right color wires. Search the archives here for guidance as to where to get the original german wire. I doubt this is the cause of your trouble but it's extremely useful when diagnosing electrical problems, and future owners will thank you . . .

Sorry the car is a 77 with an 81 sc engine in there. I did all the wiring conversion and will check my conections again. I will try that 14 pin connector and boy the wires do tend to pop out! Thanks it looks like the connector is probably the problem or some grounding back there

Ben

bad alt diode

Man the guy that rebuilt checked all of that when he redid everything 100 miles ago. He has rebuilt a couple for me in the past with good success. Maybe he will be redoing this one. What should I read for voltage at idle??

Ben

Alternator warning light

http://forums.pelicanparts.com/uploa...1095961435.jpg

the wires WILL pop out of their slots

- with two people the risk is reduced, but the advice is very sound -- have a diagram handy

yep.. I use masking tape for that prob and open gently.

I just wanted to say that I recently bought a brand new oscilloscope off ebay for $100 (Xeltec?). 10 Mhz, single channel, perfect for diagnosing alternator problems. I've pinned down two elusive problems so far. One for me (why I bought it), and one for my neighbor. Considering what an alternator costs, even to have rebuilt, you can't beat a $100 oscilloscope to make sure that you've nailed the problem.