Blue73Shark

Stock L82 with a new battery and I rebuilt the alternator with a NAPA kit. Alternator passe the varios electrical tests and charges the battery at 14.6V when running. I did these two jobs becaucse the 6 year old battery ran down suddenly. I rebuilt the alternator because it had not been done and was not charging the battery. Car runs fine, except new battery is loosing about 0.1 volt of charge every 2 days. What I have done so far (key in LOCK position):
1) pulled all fuses, flasher at fuse panel, and ACC connector (tan wire) at fuse panel - still having a discharge
2) pulled all wires off of horn relay - still having a discharge
3) pulled red positive cable off of alternator - still having a discharge
4) pulled two wire plug out of top of alternator - NO discharge
Given #4 stopped the discharge, any clue what is causing the problem? I still have to check ignition coil & starter for possible problems, want to figure out this first.
Thanks.
Fran

4-vettes

Yup, you got a bad diode in that rebuid kit. Get another one. Pull the Alternator back apart and replace it.
This is VERY common lately.

HeadsU.P.

Not sure which yrs, maybe a '73.
Somewhat common battery drain issue was the Windshield Wiper Relay. Constantly on, draining batt.

Eliredandblack

I noticed that on my 73 the rear tiny glove box light seems to be stay on. The good news is that I had change all the inter bulbs to LEDs. I messed with the led and the stupid light-push switch and there is not a lot of room for error. I even tried putting a clear rubber pad on the lid that hits the switch. My next task will be to wire in a small pc timer board like I have done for the trunk light on my other cars, after a specific amount of time the LEDs are turned off.

Blue73Shark

Thanks. Funny, I also di the "put a rubber pad on the lid" too. That works well for me. I think it is bad diodes or voltage regulator. New parts arrive Monday to swap them out.
Fran

HeadsU.P.

In post #1 you said: rebuilt ALT and its producing 14.6V when running. That's perfect!

I don't see how a faulty diode could produce such voltage.
Look elsewhere.

Blue73Shark

Yes the alternator is putting out 14.5V at idle and charging the battery. I will look elsewhere before rebuilding the alternator again. What is concerning me is #4 in my list; those two prongs are part of the voltage regulator. Maybe it is normal that when it is plugged into the alternator, it causes a slight drain on the battery. Someone elses may have tried this and have an answer.

Fran

Richard454

Does your horn work?

If not then- I'd look at the horn relay. It will be warm to the touch.

Richard

doorgunner

KEY OFF!

Unplug theThe two wires that plug into the alternator...


Check the voltage from the one of the alt. terminals to the mating wire...is there a 0.1V drain?
If so trace the wire to it's electrical component to determine fault.

Test the other wire in the 2-prong plug the same way.

Let us know the results.

Blue73Shark

Richard454 - horn works perfectly.

Doorgunner - see attached.

Will have to do some chasing down using my wiring diagrams and also swap out the voltage reuglator. Will test diodes again as I tested them and the field coils before assembly and they all checked out.

Fran

4-vettes

OK. Let me explain this. A diode can fail in 2 different ways.
First off. What is a diode? Basically a one way valve for electricity.
Ok. One way a diode can fail is to burn open. Thus current wont flow in either direction. If a diode fails in this manner charging would be reduced, Thus Heads UP assumption that all is good as the charge rate is good.
OK. Then there's the second, and from my experience the more common way a diode fails. Basically the one way valve gets stuck open. Allowing current to flow both ways.
So the alternator still throws a charge just fine. As this is the direction the valve is supposed to be open. But on shut down the door should close so to speak. But doesn't. allowing current to bleed through.
When you unplug the 2 pronge connector the battery drain stops.
You really don't need to keep looking if that bit of information is true.
YOU HAVE A BAD DIODE IN YOUR ALTERNATOR!

kansas123

Did you disconnect the battery, then check for a drain the next day?

Blue73Shark

4-vettes: Electronic/electricity is a sub hobby of my corvette and model railroad. Your explanation is spot on.

Doing that now. Will report back in a few days. That way I can rule out if the new battery is bad.

Fran

Blue73Shark

Closing the loop on this thread. Disconnected the battery and measured the voltage for 7 days: no change.
Pulled the alternator apart and checked the two sets of diodes. 2 of 3 were bad in the "heat sink" unit (see attached picture) which I did not replace during the last rebuild. Replaced all components with new ones that I tested before installation to make sure they were good. So far, no measurable battery drain. 4-vettes is the winner-winner chicken diner!

Thanks to all that replied. Fran

7t9l82

I had to replace my ignition switch with an after market unit. If I leave the key in it my battery drains down.

Blue73Shark

Thanks. If it starts draining again, I'll check mine because one of the wires coming out of the 2 prong plug (at the alternator) goes directly to it.

Fran

7T3stinger

What amp alt do you have

Blue73Shark

61 amp. My car came with air conditioning and the heavy duty battery option, both requiring a 61 amp alternator.

Fran

augiedoggy

I had this same issue with a brand new ebay alternator and replaced the diode with a napa unit to repair mine.. seller ended up refunding me like half the cost of the alternator so I didnt mind installing the napa kit soo much.