Parasitic drain? How to find? Still not fixed!

dwcopple · Jun 11, 2022

2000 GT. Diehard Silver battery dated 12/20. Tested good at 2 different Advance Auto's. New 130A alternator from LMR tests good. Charges when running.

Problem: battery dies overnight. WTF? Car has aftermarket amp/sub with power lead hooked to the main power lead on the underhood fuse block. I am going to test the remote wire with a test light today to make sure it is switched and not constant. Car had an aftermarket KARR alarm on it that I removed thinking that it might have been the culprit. What else can I check?

ttocs · Jun 11, 2022

first question is how did you test the battery? You need to remove it from the car/disconnect it and then put it on a charger. When it is done you can test it right off the charger if you want, but I would suggest leaving it alone for a few hours/over night if you can still disconnected and then test it in the morning. I have seen batteries that tested good right off the charger and then a few hours later had lost voltage while not being hooked up, and then tested bad.

To test for a drain you again start by disconnecting your battery. It does not matter if it is the +/- just pick one and remove the lead from the battery. Now get out your multimeter and set it for current which will either show A/mA or possibly "I". It is also not uncommon that on some meters there will be 2 places for the positive lead to go in to the meter and if you look next to them one should say V/R and the other mA/I, put the lead in the mA/I port. Now all you need to do is connect one of the leads on the meter to the now disconnected battery terminal, and the other to the wire that use to be attached to it so the meter is in the middle. At this point take a reading and your current should be close to 0 but 5-10mA current is not uncommon to retain the radio/ignition memory. If it is higher than that then you go to your fuse box and just start pulling fuses and watch the display. At some point the meter should show the current drop down, at that point you have isolated what circuits might be the drain by looking up what gets power from that fuse.

In the sn95's the mach amps are known battery drains. If you peel the carpet back on the drivers side console under the radio you might be able to see if the mach/premium sound amp is still installed and disconnect it if it is.

07GtS197 · Jun 11, 2022

If it’s neither the battery nor the amps take a look at the alternator. I had a brand new one drain the battery on my old 09 P71. The diodes can be bad right out of the box causing a drain overnight. Funny thing for me was the car could sit out all day and be fine but as soon as it sat overnight it would flat out die.

dwcopple · Jun 12, 2022

Well, car started this AM. As far as testing the idiots at Advance Auto do it with a tool while installed in the car. I unplugged the Mach amp this morning under the dash and luckily still have music. What does that little amp control anyways?

ttocs · Jun 12, 2022

it was really more of a cross over but it also had the amps for the tweeters.

dwcopple · Jun 12, 2022

ttocs said:
it was really more of a cross over but it also had the amps for the tweeters.

I removed the entire rear shelf setup today and installed 6x8 Pioneer 4 ways I had here in the now empty shelf and tapped their leads to the prior tweeter leads (full-range). Sounds better than before, lost a lot of dead weight, and hopefully solved my drain issue too!

dwcopple · Jun 17, 2022

Well, it's not the Mach system. Car is dead again. I reached out to LMR about this alternator. I'll try the test listed above this Sunday. Pull under hood fuses I assume?

ttocs · Jun 17, 2022

next time you park it disconnect the alt and see what happens if you leave it disconnected.

The fusebox under the hood is a good place to start. Some of those fuses go into smaller fuses under the dash but that will show up later in the testing when the fuse under the hood shows what to check. If none of them do anything then try the fuses under the dash as well.