Alterantor light stays on dimly 12v idle 13v driving.

[jsimpson]

Alternator light stays on dimly. 12 volts at idle, 13 wile driving. Hints?

 

[Stingray6974]

Yep, bad alternator.

 

[jsimpson]

Rats! well, as long as it's keeping the battery charged, I'll keep putting it off.

 

[FrankM]

check regulator first
can have a bad diode in alternator too

I have also seen this with a shorted cell in the battery

 

[jsimpson]

Frank, I also cleaned the plug and contacts. Wouldn't a shorted cell cause considerably less cranking rpm?

 

[FrankM]

John, a partialy shorted cell could do it. You can read the battery voltage when the car has been sitting awhile,(turned off) especially when hot. 11.8 is ok.

Then I would check the alternator output with a load tester.

Sometimes auto zone has the tools to borrow.

 

[barrier5]

Most likly a diode went south.But as long as it has to come off anyway might as well have it checked.

 

[FrankM]

Most likly a diode went south.

Thats where I would place my bet too..:s

 

[jsimpson]

With the AC on high, the fan REALLY draws some current, and with the electric fuel pump constantly running on the TPI, I wouldn't be surprised if I finally cooked a diode. It might be time for a higher capacity alternator!

 

[inferno-vette]

This happens a lot in old cars but it isn't a big geal any shop would fix it easly and cheap!
Paul

 

[jsimpson]

Local alternator shop is rebuilding it for $56. He says the current standard diode plate used for rebuilding ups the output from 63 amps to 75 amps. It'll be ready tommorrow. Not bad, considering it's the orinal 24 year old alternator!

 

[FrankM]

was there an actual problem before the rebuilding?

 

[jsimpson]

24 years of use, noticeable play in the bearings (but no noise), and low voltage output (max 13v, less than 12 at idle).

 

[jsimpson]

Just got it back. They replaced diode plate, stator, bearing, bushing. The case was bead blasted and they used a better condition (correct size) pulley and fan which they cad plated. The only thing they reused was the case, and they charged me only $39.95, and I got it back in less than 24 hours!!! I don't think anyone could beat that! Davie Battery and Alternator, Davie, FL 954-581-5338

 

[inferno-vette]

great price! is he your friend?
Paul

 

[jsimpson]

He is NOW!

 

[FrankM]

Just got it back. They replaced diode plate, stator, bearing, bushing. The case was bead blasted and they used a better condition (correct size) pulley and fan which they cad plated. The only thing they reused was the case, and they charged me only $39.95, and I got it back in less than 24 hours!!! I don't think anyone could beat that! Davie Battery and Alternator, Davie, FL 954-581-5338

Whats your voltages now?

 

[jsimpson]

a little more than 13 at idle or any speed. Alternator light has no glow at all.