Bad alt with no alt light?

[doclees]

OK folks no one seems to be brave enough to chime in on these electrical issues I have in other threads. How about this?
Can you have a bad alternator without the battery light coming on?
Can you have a bad battery that produces a battery light?

 

[Rob94]

The idiot light's only function is to come on when the signal from the alternator drops below, or rises above, a certain voltage. The battery can be junk...as long as the alternator is putting out a proper charge, the light won't come on.

 

[doclees]

Here is the update: Pulled battery from 89 SHO. Charged overnight on bench charger. Started great. No alt light. Got it home. Voltmeter reading 12.5x. Took it to Advance auto and had system checked. Battery was a little low but good and taking charge. It had sat for 4 months. Alt only putting out 12.5 volts so that is low and amps were 165. But then he said his equipment said no output. So maybe it is on the way out but not dead. Just enough charge to keep the battery alive most of the time?
In the olden days we had separate regulators. This is what they did when they went bad. You could jump the contacts with a no start like this. Never had an alt die a slow death.
I guess if I pull it and have it bench tested it will rule out a connection or drain issue.

 

[Phoenix]

Your alternator has something , you should read 13.7 to 14.4 V Engine running Idle.

And yes I've seen alternators going bad without the infamous light.

And no the light wont come up if your batt is toasted. That light will light up only in the case of a defective alternator.

 

[TankII]

I just posted this response to another nearly identical post.

TankII
--------------------------------------------------------------------------------

Similar problem just happened on my '91.
Turned out it was the rectifier assembly. My rebuilder found it during testing.

BTW, when he got done with the unit, it was putting out over 100 Amps.

International Auto, 16 Spring Street West Hartford, CT 06110
(860) 953-6999
Ask for Peter (the owner)

Granted, I dropped it off, but the turnaround was three days. He always uses new parts, so the bearings, brushes, regulator, and rectifier were replaced. Most rebuilders just do the bearings, regulator and brushes, hence their minimal pricing.


TankII

 

[doclees]

Thanks folks, the light has been coming on more consistently now. I am convinced enough now that I ordered an Advance auto rebuilt which I will have tested before taking it home. I sill have the old one bench tested to be sure it is not a connection. I hope to have it all back together Sunday night.

Tank what did the rebuild cost? I thought my replacement puts out 120 amps. Do the gen I put out less?

Yes I have posted this with a different title. I wasn't getting any hits.

 

[wood_e]

I had my alt in my old ATX rebuilt for about $75 at a local place.

 

[projectSHO89]

OK folks no one seems to be brave enough to chime in on these electrical issues I have in other threads. How about this?
Can you have a bad alternator without the battery light coming on?
Can you have a bad battery that produces a battery light?

Answers: Ok, Yes & Yes

 

[doclees]

Ok folks this is the update. First thanks for the direction from all. I appears to have been a bad alternator. I believe this has been going on for a couple of years. Things that seem to have fixed it in the past usually included disconnecting the battery to do. I think that would clean up the connection just enough to allow the alternator to make threshold.

I think I was lead astray last fall with a "bad starter" because after 6 shots of juice on the bench test it smoked a little. It was fairly covered in oil leakage from the valve cover gasket when I brought it in.

The bad ignition switch was also plausible because the key switch did get stuck a couple of times and was getting ratchety in turning. Upon removal and dissection it was making connection.

My new alternator is now putting out a strong 14.5 volts. all is good.

 

[doclees]

Here we go again. All was good for this week with the new alternator. Just got back from shopping 8 miles away. Came out of the store and same issue. I had tools with me so I pulled the ground off the battery and re-seated it. No change. I pulled the ground and disassembled the positive cable clamp head from the cable and cleaned some of the green oxidation off of the fibers. Put it back together. Starts right up. Get home, stop the car and try to restart it. No go. Pull and clean positive cable again after pulling ground and it starts. Shut off engine and no start again. Battery is showing 12.5 volts car off and 14.5 running.

 

[ohfosho]

you might as well replace (repair/rebuild the alternator if you wish), both the alternator and battery. one always take out the other when they get older. been through that before.

you might want to cut back your wires and put a new connection on for the battery. or replace the cables.

 

[doclees]

Thanks ohfosho. I had two issues going on. I don't know if the bad (3rd palladium) starter took out the alternator of if it was just time (176k) but my starter was the no start issue. The alt was only putting out 12.5 volts and the light was coming on most of the time by the time it was over. I have decided to pull the starter each year on a saturday, fry it, and exchange it so I don't get stuck again. I found the bad starter when replacing my battery cables. The solenoid turned in its casing when tightening the positive battery cable end. So now I have a LLT alt and starter. Maybe I just fry both each year to be on the safe side.