Soliciting opinions on a battery drain problem. The car is new to me and had a dead battery when delivered. I've done several little projects to the car over the last few months, but the battery drain remains a problem. I'll find it eventually but maybe someone has some experience with this.


In general the car is low mileage and a well kept survivor. The wiring under hood and under dash is about as original as you would find. (here's a pic). The car was owned by a collector who was very good about maintenance, so the motor has been re-painted topside, carb is freshly rebuilt, etc.


The battery drains about 0.2 volts a day. It was new a month ago, has been drained down twice now, but recharges back up to 12.8 volts no problem.


Interior:
* The fuse for the clock is removed, and I know of no other current draws, for example no light bulbs are stuck on.
* I can measure no voltage drop across any of the fuses ... 0 mV on my meter.


Underhood:
* battery cables are new and well attached. Block ground strap to fire wall is in place and looks good.
* horn relay is brand new from Fusick as the old one has disinigrated inside.
* Alternator and voltage regulator are new in the last few years. Both are currently un-plugged, but the battery drain continues.
* Points have been replaced by an ignitor LS unit and the coil is an MSD. have not tried un-hooking these yet.


So that's where I'm at so far....

 

Put a test light in series with the pos battery cable. The lamp will light if there is a current draw. Unplug the remaining fuses one by one until the light goes out. That will be the circuit to troubleshoot.

 

I can do that, but wouldn't checking for voltage at each end of fuse be the same? I've done that and none of them show anything. I'm currently (ha!) thinking the problem is in a non-fused circuit somewhere...

 

No, cause your looking for current draw from the battery per each circuit. Pulling the fuse removes each individual circuit allowing you to possibly find the offending one. There are not many unfused circuits, Starter power, horn relay, ignition and head lights (headlights have a CB in the switch).

 

Have you checked to see if the battery it self has a short ? Pull the leads off and let it set a few days and recheck the voltage for a drop. Or just take it to a good battery shop or auto store and have them check it probably the quickest .... Tedd

 

A few thoughts - since its a small drain, check single bulb areas like hood and trunk light switches, glovebox light, maplight if it has one. Until you find the problem put a Battery Tender on to save your battery. Good luck!

 

Get a voltmeter that has a current scale on it..........disconnect the positive lead from the battery..........connect the ammeter between the battery and the positive battery lead.
Now disconnect one thing at a time until the meter reads zero and you will find it.
We did this on a friends boat and it turned out to be the radio's cd motor continued to run with the radio off.

 

A fuse that is in good condition is basically a short so the voltage measured at either end of it will be the same. If a fuse were open, there would be a difference in voltage, but you are not looking for an open fuse, you are looking for a current drain on a good circuit.

 

An amendment to MrGadget's good advice above:

Disconnect all of the wires at the horn relay, then check for current flow from the battery wire to each of the wires on the horn relay.
If there is none, check the resistance between the horn relay stud and ground - if it isn't ∞, then the problem is in the horn relay. If it is ∞, then go back and disconnect the (+) cable from the battery and check current flow there - if you have a drain there, then it's somehow through the starter motor.
If none of these is the problem, then check for current flow through each of the wires that used to be connected to the horn relay. Check the Chassis Service Manual to see where the leaky wire leads, and then follow along each branch until you find the problem.

- Eric

 

Eric, checking for resistance between the horn relay stud (with nothing connected to it) and ground is not necessary as that by design is an open circuit. Any deviation of that is a short and the net result would have been smoke and burnt wires.

I do agree with doing the current check per each of the wires connected to the stud either by using a lamp or amp meter in series with each wire. I only suggested doing it at the battery because he said both the alternator and VR were disconnected.

 

I discovered one lead on my digital multi-meter coming apart, so now I don't trust some of my earlier checking. Starting over. Battery is charged and at rest today. If it measure the same when I get home I'll hook it back up and start re-checking circuits.


Work has me traveling for the next 8 days so even though you won't hear much I appreciate the responses and help. I'll update you when found!

 

So the battery has help steady for 4 days now, with only the alternator un-hooked.


I found an article on line that if you can measure any AC voltage across the battery while the car is running and charging, it means a bad diode in the alternator.
And sure enough, while running and charging I get a small amount of AC voltage measured, only about .03v but some.


All signs indicate I have an alternator problem, but the article I read was about much newer systems than a 64 Starfire. Do these old 10DN alternators have diodes in them?

 

It's an alternator. It makes AC.

The car runs of DC.

It HAS to have diodes.


Do you have a Chassis Service Manual?
The CSM gives good, step by step instructions for troubleshooting the alternator and diode board. They describe it with their GM "special meter," but you can translate that to any multimeter.

Basically, check for continuity across the diode array in both directions - you should have DC polarity one way, but not the other. Any leakage backward indicates a bad diode.

All of the internal parts of the alternator are replaceable easily and fairly cheaply, and should be readily available from RockAuto or NAPA. If you have specific questions about parts and part versions, you can ask Stellar on this board, and he will know. He can also supply you with any part, and do an excellent rebuild, as he's had a full generator/starter shop for decades.

Sounds like you're well on your way to getting this fixed.

- Eric

 

I'd listen to Eric and Eric but this poor soul had an underhood light short that drove him crazy for a while [maybe longer]

 

1964 underhood and trunk lamps are wired thru headlight switch so are nonfunctional unless park or head lamps are on.

A shorted alternator diode on these cars usually reveals itself as a GEN warning lamp that stays on with ignition OFF, but have the thing tested by a good auto electric shop and rebuilt if needed.

Your best friends here are an accurate multimeter and a good wiring diagram like the one in the factory shop book.

 

Sorry I got to the party late. It sounds like he has diode problems. Probably not open or completley shorted, but rather leaking. Unplug the alternator plug, keep the wire on the alt positive post and connect the volt meter to the alternator R terminal . If you see any voltage the diodes are leaking. This is done with the car not running with the key off. You can also remove the alt positive post wire and check to see if you have any current or voltage between the 2. Or if it is dark touch the disconnected alternator post wire to the post and watch for a slight spark. It sounds like diode reolacement will be needed.

 

I.m not sure about the AC test across the battery, but I would think almost all cars would show some AC with that test. I don't think a diode is capable of clamping 100% of the AC wave. A high reading would be a bad diode, but I don't have any specs as to what is normal and what isn't. I do remember a vehicle in the shop that had an electrically sensitive transmission that needed the wires going to the tranny to be shielded against AC produced by the alternator even thoough the alternator was perfect.

 

I did see voltage across the R terminal.
NAPA had a decent replacement alternator available but we are lucky enough to have a good auto electric shop in town, and took it there. They called back today and confirmed a diode problem. So that should be my fix.
Fix is better than replace, it lets me keep the 1100677 stamped case that is "numbers matching" for the car. Not a priority for me but nice. has a double row pulley which was quite special also.

 

That's the right way to do it. On my car the PO had "fixed" the alternator by substituting a newer internal regulated one and bypassing the regulator, it only had a single row pulley so the A/C belt slipped all the time. I had to have a new one built by Powermaster with a double row pulley and original regulator hookup, luckily the wiring was still there.

 

Hopefully (most likely) that is the issue and the repaired alternator will fix your issue.