Troubleshooting Battery Drain

[USMC67300]

Fellow C Body owners,

I am trying to track down a parasitic battery drain problem I currently have on my 67 300 w/ 440. If I measure between the battery post and cable end i get a reading of .199 VDC. I have a painless wiring kit installed by the previous owner, if i pull the 50 amp MAXI fuse it drops down to .03VDC. I have tried pulling every fuse out of the box and i can't get below a .16 VDC. My car still has the stock distributor with points, condensor, etc..The battery is a new Optima.


Thank you, 67300

 

[detmatt]

I don't have the answer to your problem but I had a similar problem with my Imperial when I got it and it turned out to be the glove box light was staying on with the door closed. I adjusted the butten that acts as a switch and solved the problem. My point is that there are a couple of places that light up when you open the other being the trunk.
Worth a check.

 

[commando1]

He said he pulled every fuse and still has a battery drain so it's not likely a light staying on somewhere. It has to be somewhere before the fuse box.
The thing that worries me is it has an aftermarket wiring kit. The wiring could be boogered 1 out of a million different ways.
Dave: lend the fellow your test light...

 

[detmatt]

True that! As I said, just suggestions and the rewire causing the problem crossed my mind but these sorts of things fall a little outside my wheelhouse.

 

[1978 NYB]

Could be a defective battery draining off voltage. Check the battery date code. My opinion only...most batteries are at the end of their life when they are 5 years old. They may charge fine when the engine is running and then discharge quickly when the engine is turned off. I would check that out first. Again ...just my opinion.

 

[polara71]

My opinion only...most batteries are at the end of their life when they are 5 years old. .

At that age they are living on borrowed time.

 

[USMC67300]

Thanks for the feedback, today I disconnected the alternator and it dropped down .04< It must be the alternator, it is a re-manufactured unit that was in the car when i bought it> If any of you guys have a minute, pull your positive battery terminal and measure what voltage you have between the post and terminal< seeing if you get 0.0 or just a little bit more, less than .05.

 

[BillGrissom]

I am a bit confused by your diagnostic technique. Is this something you learned? I would expect one would measure the resistance from the BATT+ cable (disconnected) to BATT- (connected). That would measure the parasitic load on the battery. Not sure why there would be a voltage difference when disconnected or what the voltage difference measured means. It seems what one measures might depend on the meter used. Is yours an old Simpson type gage w/ needle, instead of an electronic multimeter?

You are correct that the alternator can discharge the battery. It has 3 diodes in parallel to BATT+. Ideally, they wouldn't conduct in the reverse direction, but of course there is some reverse current flow that very slowly drains the battery. I know of no cars that disconnect the alternator to battery lead when off. Modern cars are much worse and I read that new cars left at airport parking lots >2 weeks regularly need a jump. I put a Battery Brain on all my cars, new and old.

I agree that >5 yr old batteries are suspect. I don't usually note an internal short, but rather the plates get sulfated so that they no longer hold much charge. If one is run down, you put it on the charger, and its reads fully charged in 10 min at 10 A, that is a sign it can't hold a charge. I used to get K-mart Exide batteries and return them since they had a warranty. They used to fail like clockwork every 3 years. I noticed a few batteries in my cars are >8 yrs old now and appear good, so must depend on the brand. Some swear by the Autozone Goldtop.