JSGD1966

It was a beautiful day today and I had the wife and kids all set for a Sunday drive since two weeks ago I went to start up my '66 Cutlass Convertible and the battery was dead. Oh well, I will just get a new battery I said. New battery was installed and started right up. I took one drive the next day, no trouble. It has been 2 weeks since that drive and haven't driven it since, and the battery was dead again. I am assuming the alternator/generator should be ok since I only drove it a total of 2 hours since the new battery was installed. I also know that a battery can be drained in about an hour if the alternator/generator is not working at all. I will probably pull it and have it checked first, but is there any way to locate a short or something that could be pulling current on the battery? There are no obvious signs like headlights left on, interior/trunk lights on, etc.

Any help or advice would be appreciated.

Lady72nRob71

Two weeks sitting should not drain a new battery.

First make sure you do not have a lot of accumulated greasy crud over the positive junction block.

Best thing would be to get (or borrow) an ammeter and put it in series with the battery to track the leakage. Anything over a milliamp in a car of this vintage would seem abnormal. If you have an alarm or newer radio, it may be a couple milliamps at most.
If higher than this, disconnect the alternator and start pulling fuses one by one to isolate where it is coming from. (This is done with the ignition OFF of course).

My 86 Olds had a capacitor failure in the radio which did this similar thing.
Luckily it had a tell-tale sign of the clock never going off...

BILL DEMMER

i would have the charging system tested. a new battery will usually not be fully charged. a 50% charged battery will run your '66, during daylight, for many hours, especially if it is a high-capacity battery. cars of that vintage draw only a few amps to run. at night the lighting loads would cause the battery to drain much faster. add in running the blower motor, and a fully-charged battery would drain inside of a couple of hours.


bill

Modern Motoring

Rob has it correct, but you can do this a bit simpler. Put a 12v test light inline between the negative cable and the negative post on the battery. whatever is pulling current will now also light the test light. This is great when you are in a garage with your head under the dash, just pop up for a glance at the light.

Bluevista

I know this won't fix the problem but all my cars have the battery disconnects on them. The kind that goes on the ground terminal and has a **** that turns to make contact. That prevents the battery from draining down if there is a small problem anyway. Sometimes it's as small as the glove compartment or console light being on, like a refrigerator, does the light inside ever go off?.. who knows? unplug it and everything is off for sure.


Allan

JSGD1966

All very helpful suggestions and are very much appreciated. I will try the 12v test light first. That is a pretty slick idea. I will be getting another battery disconnect. I used to have one and I used it as an anti-theft device and unscrewed the **** every time I parked the car for a period of time. I think I used it too much as the threads stripped on the **** and I had to remove it in order to get the car started in the middle of a parking lot.

JSGD1966

Well, I tried the 12v light tester as suggested above and with the key off, the light is bright and lit. So I unplugged the alternator and started pulling fuses, checking the light after each one then putting it back in if the light was still on. I went through all the fuses and no luck. The light never changed. I went to sears and national tire and battery to get the alternator checked, but they said they couldn't help a car that old. So now what? I am scratching my head here knowing the fuses were checked, I inspected the car in total darkness to see if any interior lights were lit, checked to be sure the cigarette lighter wasn't pushed in, etc. I don't know anything new. I installed a battery disconnect until I can figure this out. It really kills the confidence level, when you wonder when your battery will die again. The next step I guess is an ammeter. I have a multi-tester, but I think it is more for residential electrical. Not sure where to put the dial to test the car. 15Ma? I don't expect anyone to be able to tell me what's wrong exactly, it could be so many things. I am trying to at least find out if there is a way to isolate the drain to either the engine compartment or the interior. If I cannot get an ammeter, or get any new info from it, then I will just head to the shop and see what they say. Any additional help, tips or advice is always appreciated. Thanks for the advice so far.

BILL DEMMER

i would next check for a glovebox or trunk light on.

how high does your multitester scale on the dc amps range? set it to the highest range. some meters require the use of a different socket for testing higher current. you would plug the positive lead into a different "hole" on the meter. it should be marked(if equipped).

did you disconnect the bolted-on wire from the alternator?
also disconnect the voltage regulator.


bill

KeithA0000

I don't think that you need the ammeter; your light tester told you everything that you need to know, as far as I can make it out. Something is drawing current. I'd take the alternator to a garage that can give it a proper test. I'd guess that your problem is there. If not, a short anywhere in the electrical system could be the cause. That's a tougher bit of troubleshooting to manage. I'm hoping for the bad alternator. Good luck!

JSGD1966

Bill- Checked the glovebox, bulb must be burned out, no light anytime. Checked the trunk, bulb has been burned out there for years, no light. I did disconnect the plug and bolt on wires from the alternator when I checked the fuses. I did not try the voltage regulator. It is worth a try. As for the 8 range multitester I have, the DC-V side goes 15, 150, 1000. Then there is a RX1KΩ and 150mA DC. There is only one place to plug in the probes and the NEG side has a 500V MAX rating, the POS side says 1000V AC/DC 150mA DC MAX. All greek to me.

Keith, thanks for the post. The alternator will be coming off and get tested properly. I will more than likely upgrade to a higher amp model if it needs replaced. Just to be prepared in the future for any extra accessories I may add.

Well, back to testing. I will keep you posted. Thanks again!

Oldsguy

DC-V side reads 15 volts full scale, 150 volts full scale, then 1000 volts full scale; you measure from a test point to ground to read voltage. The RX1K is used to measure resistance and 1,000 ohms would be full scale; you measure from a test point to another test point that you KNOW should be the same wire or point electrically (with power off for safety). You don't need that right now. 150ma DC is to read current and can be measured in a number of ways depending on what you are looking for but you don't need that now either. The probes are pretty Murphy proof since there are only two, one for each probe. Using the DC-V on 15 volts scale setting should work the best for you while you are looking for any stray voltage where it should not be, but, you have already done that with the test lamp which does the same thing. When the lamp was lit, the meter would have read a voltage (probably 12 to 14 volts). What Rob described would work too, just be sure to secure one lead from the meter to the positive battery post and the other lead from the meter to the battery cable that should attach to the battery post (DO NOT ATTEMPT TO START THE CAR WITH IT THIS WAY) you will burn a test lead in a millisecond.

Jamesbo

The light under the hood are also notorious for causing problems

BILL DEMMER

that one is only supposed to get power when the parking/head lamps are on.


bill

BILL DEMMER

ok, your meter isn't going to be of much help for measuring current draw. 150 mA is about how much current a 194 marker lamp consumes. you shouldn't toast a test lead-you're meter likely has an input fuse.

sometimes the points on the electro-mechanical regulator stick closed. if the current draw(lit test lamp) was still happening with the alternator completely disconnected-that's not the problem.

does the '66 use a junction block for the power distribution? that would be under the hood, about the middle of the driver's side fender. if so, i would try using the test light from that position and disconnecting the wires one at a time. one wire should be from the battery, iirc. a '66 a-body wiring diagram would be helpful, if anybody has one handy.


bill