Time for an Alternator?

[Driver_X]

I've been chasing a glowing Alternator light and was finally able to get under the car today to check the grounding strap for corrosion. It wasn't too bad, but I cleaned up the connection to the body nice & shiny. It looked to me like the connection on the trans is near impossible to get to, so I didn't check on that one.

I then checked voltage at the battery. Car was warm. Put on new fan belt last week as the first step to trouble shooting, tension is good and no slipping.

12.65 before start, dropped to 11 something during starting and then it hung between 14.8 & 15.1 @ idle for like 4 minutes until I had my wife rev to 3,000 and hold. As soon as the revs went up, the voltage dropped to 14.5 or so. Voltage was not steady, would jump around a bit usually .3v range. Again at idle, voltage slowly dropped to 13.3 +/- and light would dimly glow. A blip of the throttle brings the voltage up, light goes out, then the voltage slowly drops back down again. I'm thinking voltage regulator.

[Bob Kontak]

Correct. Variance should be in the few hundredths of a volt range.

However, I do not know the threshold for when the charge light is intended to come on.

[Driver_X]

VR is built in to the alternator right?

[47silver]

get an adjustable voltage regulator,, your 74 should have an external vr. near the cdi, on the drivers side.

mine did the same thing,,, the alternator was rebuilt and rechecked,,,the vr was letting the voltage drop too low,, i purchased an adjustable vr and it has worked perfectly since.

[wwest]

Originally Posted by Driver_X

I've been chasing a glowing Alternator light and was finally able to get under the car today to check the grounding strap for corrosion. It wasn't too bad, but I cleaned up the connection to the body nice & shiny. It looked to me like the connection on the trans is near impossible to get to, so I didn't check on that one.

I then checked voltage at the battery. Car was warm. Put on new fan belt last week as the first step to trouble shooting, tension is good and no slipping.

12.65 before start, dropped to 11 something during starting and then it hung between 14.8 & 15.1 @ idle for like 4 minutes until I had my wife rev to 3,000 and hold. As soon as the revs went up, the voltage dropped to 14.5 or so. Voltage was not steady, would jump around a bit usually .3v range. Again at idle, voltage slowly dropped to 13.3 +/- and light would dimly glow. A blip of the throttle brings the voltage up, light goes out, then the voltage slowly drops back down again. I'm thinking voltage regulator.

That all sounds SOP to me...

Any indication the battery isn't being charged well enough to crank the engine on the next restart should be of concern.

Otherwide...sleep well.

The only possible anomally is the dim glow of the bulb at idle, but since it extinguishes with rising RPM...

Your alternator has three output phases/windings internally, and a "Y" bridge rectifier, one of them having failed "open" and you would see that dim glow at idle. failed "shorted" and teh alternator will overhear and soon fail.

[rick-l]

Isn't a dim light while running a sign of a shorted diode?

I haven't figured out if it is 3 or 6 phases since there are 16 big diodes in my 88

[ppanagis@gmail.]

is your car ideling steadly or does it drop after a few seconds. I had the same issue but turned out that my car needed point adjustment and a slight timing... just a thought.

also what are you ideling at?


Another thing to notice? you mention 15.1 volts that seems too high... if all else fails i would try a VR