Surfer69

Something is killing my battery in only two days when sitting. I'm not good with electrical things.

I've looked everywhere but see nothing shorting. How do you use the fuse box to try and find it with meter?

Or if diode in alternator or something is shorting out how could I tell?

Thx

Jebbysan

Remove the negative bat cable and run a test light in series. One end on the cable and one end on the post itself. If there is a draw.....the light will come on.
From there....start pulling fuses in the fuse box until the light goes out. This will narrow down the circuit. From there you will have to find the culprit by poking around that circuit.....seeing if anything is out of place or looks bad.

Jebby

C6_Racer_X

I use a digital multimeter. Mine will measure up to 10A on a special input point for 10A. I plug the red aligator clip probe into the 10A port on the meter, and I have a special black wire that I use. It has a 7.5A fuse in an inline fuse holder, and it ends in a big clip like the ones on battery chargers.

I disconnect the negative battery cable. I clip the fused black wire to the negative battery terminal on the battery, and the red aligator clip wire to the negative cable leading to the car. If it doesn't pop the fuse (I hope), I check the current reading. Anything under 100mA isn't horrible. Under 20mA is good.

If there's a bigger current drain, but not enough to pop my protective fuse on the black wire from the meter, I start out pulling fuses one at a time and checking the meter. When the drain drops when I pull a fuse, the draw is on that fuse. If none of the fuses find the draw, I start on the unfused stuff like the alternator charge wire, the alternator low voltage (exciter) wires, and some of the other unfused stuff in the engine compartment. Here you really need a wiring diagram for your specific vehicle.

If the draw is so big it pops the "external protection" fuse in the meter lead, you can pull all the fuses bigger than the one in your black lead from the meter first. Put a fresh fuse in the black lead from the meter and see what happens. If it doesn't pop, then it's on one of the fuses you pulled. Put them back in one at a time until the fuse pops. Watch for increases in the draw from each circuit. When you hit the "really big draw" circuit, the fuse in the meter lead may pop, and you know that one is drawing over your external "meter protection fuse."

Big2Bird

I have a test light with alligator clips on a 20' zip cord. I can carry it around while pulling fuses or connections on the car, a motor home, or whatever.

Big2Bird

BTW, bright light is large draw, dim light is low draw, such as a radio memory feed, ecm memory, etc.

I use a trailer lamp. Don't use an LED, use an old fashioned incandescent lamp.

MelWff

have you eliminated a bad or old battery by having it load tested?

Fredtoo

Unplug the alternator, and disconnect the big wire that goes to the back.

If the battery does not go dead as fast, you have narrowed it down.

(there may be more than one item that is draining it)

7T1vette

Stick your volt/ohmmeter in the battery circuit like described above;

Remove the interior lamp bulbs so the door can stay open while doing this work (without having bulb current flowing);

Remove all the fuses...but keep track of where they should go;

Meter should read less than 100ma (unless you have a digital radio with constant ON feature for clock display)--if much higher than that with the fuses out of the fuse block, you likely have an alternator problem;

If meter reads zero or very low current flow, insert one fuse at a time until you find one where the current reading shoots up;

Continue process, noting which circuit shows increase in current flow.

This should help you identify WHERE the current drain[s] are located. Use similar process on just the "problem" circuits until you narrow the problem down.

P.S. If you have added other electrical equipment to the car (upgraded stereo, electric coolant fans, etc), those are most likely areas of such problems.

Buccaneer

You can use a multi-meter as well.

OldCarBum

Check the simple stupid things first. Light in the rear compartment going out when lid is closed. Dash lights off, make sure brake light or turn signal isn't staying lit. Disconnect your battery both positive and negitative, put a full charge on it and see if it holds a charge. Clock, radio not shutting off, etc. check all your grounds. Do as suggested above. Good luck.

Peterbuilt

At the starter solenoid any chance that you connected the BLACK ground wire to the top positive terminal instead of to a bell housing bolt?

Surfer69

Thanks guys, good stuff.

Right now all I did was check battery which is new Die hard and shows good voltage at 12 something. When running it shows 14 so alternator seems OK.

Went around checking interior lights etc...and nothing is on. I will have to try the disconnect battery and check fuses thing then next.

Everything was fine just a week ago so it has to be something new that happen. I was fiddling with lighter so checked that too and made sure no wires are shorting.

Fredtoo

The alternator can still charge the battery, but cause a drain when the car is off.
I am having that issue myself.
Replacing the diode trio helped, but did not fix it.
The internal regulator is next on the list.

The only way my CTEK charger can top off the battery, is when I unplug the 2 wire connector on the alternator. If I leave it on, it slowly drains the batt.

Surfer69

OK so I took negative off bat and put test light in series between neg terminal and neg clamp after pulling interior bulbs out. Light when on. Then pulled each fuse one by one and light still stayed on.

Pulled two wire plug out of alternator and light went out but not sure that means anything. Need more help. Might just get new alternator now?

7T1vette

If you only have a test light, I believe that is what you should try next. Remove the alternator and take it to a reputable business source that can check it. Look for a starter/alternator shop in your area; that's your best choice. Taking it to a national chain car parts store is NOT the best thing you can do...but that may be what you are left with.

From your diagnostics, it sounds like one (or more) of the diodes in the alternator has "thrown craps" and is allowing DC voltage to drain through it. Whoever tests the alternator needs to have some knowledge of checking for a defective diode pack within it.

Kingtal0n

alternating current is seen as a ground to DC current, so when the diode trio fails this is how the warning lamp comes on in the dash, DC 12V from one side of the bulb goes to ground through the trio.

When the engine is off, there is no Alternating current being produced. So I am not sure how the DC would ground through the trio (Would have to take another look at schematic but off the top of my head Im not sure tis possible) although now that I think about it I think that the alternator light coming on when the ignition is off has something to do with this pathway NOT having any AC at the time. What I think I was trying to say is that the 12V DC is coming from the ignition, and would light the bulb if it were a drain. Which eliminates that wire.

C6_Racer_X

That definitely means something.

Your 69 still has the external voltage regulator, doesn't it? Further testing is required to diagnose whether it's the diodes in the alternator that have failed, or if it's the voltage regulator that has failed and it's leaving the stator coils energized when it shouldn't.

It's been a long time since I've worked on a 1972 or older Chevrolet, so my memory on that is foggy. From possibly faulty memory, I suspect the regulator more than I'd suspect the alternator at this point. For some reason I'm thinking if the big charge wire is the drain, it's the diodes in the alternator and if the smaller stator ("exciter") wires are the drain, it points at the voltage regulator as the failing part. I'm not sure that I'd trust my memory on this over someone who deals with these older electrical systems more often.

IMO You really need to find a well established (old) "automotive electric shop" or "starter and alternator shop" and take at least the alternator there (maybe the whole car if that's possible). I'm not sure that a chain auto parts store will be able to fully test your alternator.

Surfer69

OH by the way I accidentally touched both battery terminals thinking I was checking voltage but I was set to AMP and the fuse fried. So cant check amp right now.

Surfer69

That could be and issue since I have noticed my key cylinder seems to be acting up. Not sure if thats what you mean but if new alt (cant find good Delco right now, special order) is put in and same symptoms show up then its ignition. Thx

andyanth

Youve probably thought of this already, but put a kill switch on the neg batt cable. Every time you leave the car, open the switch. Its a good temporary solution until you find youre problem.