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

J

jsimpson

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

jsimpson

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

FrankM

Well-known member
Joined
Nov 4, 2001
Messages
154
Location
Derry, NH
check regulator first
can have a bad diode in alternator too

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

jsimpson

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

FrankM

Well-known member
Joined
Nov 4, 2001
Messages
154
Location
Derry, NH
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

Well-known member
Joined
Dec 27, 2001
Messages
126
Location
janesville wi usa
Corvette
1982 bright blue coupe
Most likly a diode went south.But as long as it has to come off anyway might as well have it checked.
 

FrankM

Well-known member
Joined
Nov 4, 2001
Messages
154
Location
Derry, NH
barrier5 said:
Most likly a diode went south.


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

jsimpson

Guest
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!
 
I

inferno-vette

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

jsimpson

Guest
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

Well-known member
Joined
Nov 4, 2001
Messages
154
Location
Derry, NH
was there an actual problem before the rebuilding?
 
J

jsimpson

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

jsimpson

Guest
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
 

FrankM

Well-known member
Joined
Nov 4, 2001
Messages
154
Location
Derry, NH
jsimpson said:
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?
 
J

jsimpson

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

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