Electrical Issue (battery draining over 2 nights)

[GT99BLACK]

Hi guys,

New here but searched this forum and others and also checked the FAQ before posting. I recently purchased a 99 GT. I drove it 200 miles home and I was driving it every day. I have had no problems with the car when the battery is charged. It is not my daily driver so I let it sit for 3 days and when I went to start it, it was dead (no click, nothing). The battery is brand new and there is a new alternator (previous owner told me the battery was draining but he would just get a jump if he needed it). I used a low current clamp to try to find the problem by pulling every fuse one by one and did not notice any change in the drain. I do not have experience in electronics so I will tell you how I did this: I put the fully charged battery in the car, did not start it, then, with the driver side door open, pulled all the under dash fuses one by one while a friend read the meter and then I pulled the under hood fuses. No fuse pulled changed the reading on the meter. The meter read 1.13 the entire time and occasionally went to 1.14,1.15 but it didn't seem like it was related to the fuse pulling/not enough of a change. I used this meter: http://www.amazon.com/dp/B000W8HD6O/?tag=stangnet-20

Anyway, noticed the ground cable from the battery to above the DS headlight had a lot of electric tape (picture attached, already ordered new battery tray) but my friend said a bad ground probably won't drain a battery but that I should fix it.

I have a couple of questions:

1) Any ideas how to approach the drain, do you think I was using the clamp incorrectly or was having the door open/not letting the car sit for 40 minutes a problem?

2) I can't find where the ground connects to the engine. I was thinking the first step would be to make sure my grounds are good. Does anyone have a diagram? I know that my hood ground strap isn't connected to the frame but I was pretty sure that isn't the problem.

Thanks to anyone who reads this/has any input. Any info will be greatly appreciated!

 

[wmburns]

No fuse pulled changed the reading on the meter.

Let me ask you. Does this make any sense? No change at all? IMO, it's more likely the meter is on the wrong setting (AC/DC), the wrong scale or not zeroed correctly.

I would want to know that the test meter is given reasonable results. For example, closing the door should make the reading change. Opening the door should make it change back.

Regarding the engine ground strap. It's located on the left hand motor mount and goes to the left hand frame rail.

FWIIW, the usual causes of drain are radio (and radio mods) and electric seat. Sometimes the electric seat switch will get stuck on.

Your friend is correct. You should fix the ground. I agree that it won't cause a drain. But it could cause the battery to not get changed in the first place.

 

[GT99BLACK]

Thanks so much for the reply. I think you're right about user error with the clamp. Thinking about it now I think I didn't zero it correctly because opening closing door didnt change reading much, if at all. Going to try again this weekend and will update here. I had meter on DC setting but will do some research on zeroing clamp properly/clamp settings.

 

[z28forlife]

You need to do a voltage drop test. Measure each circuit and see what the voltage drop is to see if there's a drain. If non show up then it might be a bad pcm or dme that's draining after the car goes to "sleep" You'll have to let it sit for at least 45 min then test the different ecu's.

 

[GT99BLACK]

Thanks for the info. I figure I might as well ask, which setting would you use to do the reading with the clamp? I am now sure I was using the wrong setting the first time around V(DC/AC) using the DC setting which would measure volts I assume and I need to measure amps (feel like a jackass now, ha).

 

[wmburns]

Use the 4 amp DC setting (the dash/line symbol). A car's system is DC. If the meter is set to AC, it won't read anything but AC ripple.

As stated before, the meter needs to be able to detect rather small amounts of current. So if turning on the dome light does not change the reading, then likely the tool is not senstive enough to do the job.

The write up talked about the importance of "zero"ing the tool. I believe it stated that the clamp on amp meter needed to be in place when zeroed.

RTFM anyone?

You are on the right track.

 

[GT99BLACK]

Haha I promise it's the worst FM. Nowhere does it explain any setting and the part about car battery drain is VERY vague just says to clamp on negative cable and take measurement. Thanks for the help!

 

[gatrus]

Let me ask you. Does this make any sense? No change at all? IMO, it's more likely the meter is on the wrong setting (AC/DC), the wrong scale or not zeroed correctly.

I would want to know that the test meter is given reasonable results. For example, closing the door should make the reading change. Opening the door should make it change back.

Regarding the engine ground strap. It's located on the left hand motor mount and goes to the left hand frame rail.

FWIIW, the usual causes of drain are radio (and radio mods) and electric seat. Sometimes the electric seat switch will get stuck on.

Your friend is correct. You should fix the ground. I agree that it won't cause a drain. But it could cause the battery to not get changed in the first place.

I had the exact same problem with my 98 GT. By removingone fuse at a time in my engine bay. i Found it to be my fuel pump that was the battery drainer. Now we must have 2 fuel pumps because after removing the fuse, the car still starts. I now have to do some trouble shooting at the pump area. At least I don't drain my battery any more. I just remove my fuse. I usually drive my car about twice a week depending on the weather.
Hope this helps

 

[Abb0]

There maybe other fuses around. If the meter isn't zeroed correctly you'll still see a current drop.

 

[GT99BLACK]

Okay guys, worked on this today. Thanks for the help! Left car for at least 45 minutes then made sure meter was working properly by opening the door and noted reading went from .0079 to .0082 then started pulling fuses. Pulled every fuse under hood/dash with no change in the reading then closed/opened the door to make sure meter still reading properly. The manual for the meter said reading of normal car is 40 milliamps so I'm thinking my car is 79 milliamps. Is that right? Not sure what to do next but I'm sure meter was working properly and sensitive to read change of dome light on. Any ideas?

 

[98stanggt22]

Okay guys, worked on this today. Thanks for the help! Left car for at least 45 minutes then made sure meter was working properly by opening the door and noted reading went from .0079 to .0082 then started pulling fuses. Pulled every fuse under hood/dash with no change in the reading then closed/opened the door to make sure meter still reading properly. The manual for the meter said reading of normal car is 40 milliamps so I'm thinking my car is 79 milliamps. Is that right? Not sure what to do next but I'm sure meter was working properly and sensitive to read change of dome light on. Any ideas?

i see you are measuring amp. i think you should try and measure in resistance to all of the connections from all the ground wires and all the connections of the battery alternator and ecu. you should also check the resistance within the fuse box also. the resistance when measuring the connections especially that taped up battery ground, should be very minimal. and also with the ground, if the previous owner altered the factory wiring, you need to make sure the power and ground wires are the same guage for the battery and alternator. i have one question, did the previous owner install an underdrive pulley system? if so you are going to need a HO alternator or the original alt pulley because it wont charge the battery properly because it doesnt spin as fast as needed.

 

[wmburns]

Just wondering. Did you CONFIRM that the alternator's output is correct and the battery is charging? Have you confirmed that the battery is fully charged and is capable of holding a charge?

Did you repair the ground wire? Did you confirm that the grounding strap between the left hand motor mount and the frame rails is in place?

I have to say that if your load were 79 milliamps, that will not run down a fully charged battery in three days.

There are 1000 milliamps in an amp. So 0.0079 amp is 7.9 milliamps!

How much does the load change if the radio is turned on?

OBTW, a typical dome light is 10 Watts. At 12 volts, a current of 0.833 amps is required. This is Ohm's law (Power=current*volts). This is 833 milliamp just to run the dome light. Almost a full amp just to run ONE dome light.

Your measurements have the dome light using 3 milliamps. To me this says that your meter is not accurate enough to measure the low currents required to correctly nail down this problem. Consider using an old fashion "shut" style amp meter.

 

[GT99BLACK]

Previous owner did not Install underdrive pulley but did install alternator. Thanks for the advice and I will look into measuring resistance.

 

[GT99BLACK]

I have confirmed battery is fully charged (using charger until notifies me batt is full) but have not confirmed it can hold charge(seems to hold fine if batt is out of car but I'll go get it tested) and dont know if alternator output correct. I have not replaced the electrical taped stock ground so it looks like I have a bunch to do. I really appreciate the help and will go through all these steps before asking anything else. I feel like meter is jacked up or user error again to get such a low reading. Have to wait until Saturday to get under the hood so will let you know and hopefully find the issue. Thank you!

 

[98stanggt22]

I have confirmed battery is fully charged (using charger until notifies me batt is full) but have not confirmed it can hold charge(seems to hold fine if batt is out of car but I'll go get it tested) and dont know if alternator output correct. I have not replaced the electrical taped stock ground so it looks like I have a bunch to do. I really appreciate the help and will go through all these steps before asking anything else. I feel like meter is jacked up or user error again to get such a low reading. Have to wait until Saturday to get under the hood so will let you know and hopefully find the issue. Thank you!

one last thing, its a simple task since you have a multimeter or whatever you are using measure the battery directly. also while you have a few things to do try a voltage drop test.

 

[GT99BLACK]

Small update: been busy with work/other things but I had my driver's seat reupholstered and the power seat was working when I took it to the shop but not when I got it back (of course with the seat moved all the way forward so I couldn't even get in the car). When I got the seat back from the shop and put it in my car, the fuse was blowing every time I connected my seat to the harness so knew I had to find the short. Took the whole thing apart (also you can adjust the power seat manually, might do a write up to make some sort of contribution here) and then I was checking for which harness was blowing the fuse by plugging them in one by one and the fuse didn't blow this time around. I now have the seat where I want it and unplugged the main harness from the car to the seat. I have a feeling this is what may have been draining my battery. Will find out when I check if the battery drained over a few nights of the car sitting. Thanks again for the help.

 

[GT99BLACK]

Another update. (been super busy with work) - Long story short, I was able to fix the ground with the help of a local mustang shop. They recommended a shop that deals with electronics only for the drain and I had to pay $84 but the guy there said it was fuse #27 (radio) which was draining the battery and he was able to pinpoint the problem to one of the amps on the back speakers. I pulled the fuse since I don't use the radio (this was last Saturday) and the battery is still holding its charge and everything seems to be good to go 8 days later. I'm hoping it's not an intermittent issue since I wasn't able to find the drain and a guy a few booths down from the mustang shop couldn't find the drain as well. This battery has issue has caused a problem with my tune (93 octane, bolt ons, etc) where it's idling terribly so I'm having the mustang shop I went to do a custom tune for me. I wanted to thank anyone who responded for all the help and just give an update on what happened. Also, posting a pic of my car as it looks today.