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What is draining my battery?

New User
Posts: 1
Joined: 02/13
Posted: 02/24/13 08:32 PM

Hey guys... Having a bit of an electrical issue with my 87 gt. 5 speed manual.   Bought a new battery.. Hooked it up. Started her up. Let her run for about a half hour. Put her in the street. Turned her off.  Went to pull her back in and no start.  Battery was drained.. Jump start.. Let it run for a while.. Cut it off.  Crank it and nothin.  The only thing I can think of is m y alarm.. But that Clint possibly drain a "new" battery in 30 mins.?   So now I have it hooked up "just the battery" to a small charger... It's been on there for 15 hours and still "charging"   .  Havnt had it running long enough (sense I thought about the alarm) to turn it off.    Last time I jumped it..  It died while running.. And no power.  Anyone got any ideas?   Thanks in advance.  I'm stumped.  


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Posts: 96
Joined: 04/12
Posted: 02/25/13 06:45 AM

please disconnect the battery charger now...

lets go thru a very needed set of tests.....  you will want to print this image... and follow it...


VOLTAGE Drop Testing


post your results by number...





Post Reply
Posts: 96
Joined: 04/12
Posted: 02/25/13 06:55 AM


roll down the drivers window...

lock the car like you normally ***

hook your digital volt meter up to the 10 amp DC or greater setting.  warning this requires moving the wire from one hole in the front of your digital volt meter to another just for this 10 AMP DC , 15 amp DC or 20 amp DC setting...

disconnect one test lead and place your digital volt meter test leads between the cable you disconnected and the post it was disconnected from...

Current Draw

an expected reading on any car with a computer will be 0.030 amps DC...  thats 3/100th of an amp...  thats keep alive memory for the computer and the car stereo..  

i have seen car alarms take significantly more and drain the battery in a few days when the car is not driven...  

Post Reply
Posts: 96
Joined: 04/12
Posted: 02/25/13 07:14 AM

the tests i have posted above can be done in under 10 minutes..  and are NEEDED unless you want to spend HOURS or DAYS chasing GHOSTS...

i answer a LOT of posts here..  you are going to have to trust me and follow these instructions in order..

depending on which alternator you have...   if you have the one with the 2 black quick connect plugs on the back.. you might want to unplug the voltage regulator connection if you get more than the 0.030 DCmA draw...

next... i would like you to invest 4 bucks in a decent wooden handled stainless steel wire brush..


see how your mustang is wired...

Mustang Starting System5

with the battery disconnected.. count the wires on the starter solenoid on each terminal..

remove one nut at a time and wire brush each side of the ring terminals and the posts.. put it back together and go to the other side...

clean the battery cables.. both at the battery and where the ground wire attaches at the block...

you can see the various ground connections in green squares in this image that need cleaning..


a ground is not really a ground on a car.. its half the circuit and the side that supplies electrons..

as electrons flow from negative to positive ,  if you have a bad ground .. you won't have enough electrons to operate the circuit...  

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New User
Posts: 5
Joined: 02/13
Posted: 03/04/13 10:39 PM

You could try pulling the fuse from one holder each night.
I would start with the biggest power drainers, i.e. the
alternator, then brake light switch, etc, etc.

Bob aka-pepsi1  

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New User
Posts: 4
Joined: 07/13
Posted: 07/08/13 10:53 PM

might be your alternator i had this problem with my 88 lx  

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New User
Posts: 41
Joined: 03/13
Posted: 07/08/13 11:39 PM

this is all PROFESSIONAL TESTING.. if you can find a professional mechanic..  who is interested in FIXING your car.. instead of just throwing parts at it..

and yes.. the alternator can be bad..

but how many alternators would you like to install.  

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