Battery Draining Need Help!
 

Ok so, bear with me. Recently my car has been draining the battery after setting for only a couple days. It’s been about 3 years since the last battery so I thought I might have been the battery, I replaced it and it’s still doing the same thing. Before I got it, that fans have been wired to run when the ignition is on, and an aftermarket radio was put in. Since I’ve gotten it, I put in after market combo lights, replaced the fans with rx8 fans (1 was locked up) and that’s all electrically speaking. I would like to trouble shoot it and figure out what’s causing it but I have no idea where to start....idk if they have common wiring issues, or just a place to start in general, thanks for any help!

First, make sure that the radio and interior lights (dome, glove box, rear hatch) are all off when you remove the key and exit the car.

9 times out of 10, it's aftermarket electronics. Bone stock cars don't usually have problems. I have seen messed up pop up headlights that get stuck and the motor is still running trying to move the headlight, that's about it on a stock car. Most likely something aftermarket is a problem or something dumb like Resterof said, a light that is staying on or something.

Humble Mechanic has a good how-to on finding parasitic draws -


Dale

Great info, thanks guys! I’ll start there and see if I can find anything

My nearly bone stock FD with > 7 year old battery will start without issue after 3-4 week hibernation.

This was a fun video to watch to demonstrate how much aftermarket wiring could be removed

Wow mine will set for about a week and be dead. I checked to see if there was any draw on the battery and it measured 0.15 amp, can anyone confirm if this is normal? Or should it be 0.00? On the videos they were saying a 2-4 amp draw would kill your battery

I've never measured the dark current on my '94, but during the winter it sits for extended periods in a garage that has no electrical service, so no trickle charger. The battery (Optima Red Top) slowly discharges but will still start the car after a few weeks. I found that the battery lasts longer if the factory alarm system is not activated.

The '94 factory service manual at page G3 says that dark current should be 20 mA (0.02 Amps) or less.

thanks for the info! That’s what I was wondering. So at 0.15 dark current, it should be fine. I’ve also done some reading saying that is the alternator is bad and can discharge the battery? With the dark current being within spec, that’s the only other thing I can think of, unless I’m overlooking something

What units are you measuring? Are you seeing 0.15 amps or milleamps?

1 amp = 1,000 milliamps, so if you are seeing 0.15 amps, that converts to 150 milleamps, which is way more current draw than the 20 milleamps spec.

good point, I’m measuring on the 10amp setting on the multimeter, so you’re right it would be 150 milliamperes, I was off by a decimal, thanks for catching that. So in reality based on my setting it should read 0.02 or less correct?

Yes, with the meter set to measure at that 10 amp range, the car should be drawing at or below 0.02 amps. However, when a meter is set at the 10 amp range, 0.02 amps is probably too small a value to measure very precisely. Instead, can you set the meter to a lower range, say 1 amp, or better yet, does it have a milleamp (mA) range?

On the other hand, if you now are seeing a dark current of 0.15 amps with the meter set at the 10 amp range, the meter is precise enough to tell you what you need to know -- that the car's dark current is excessive. Something is drawing too much power from the battery. As Dale said, it is probably aftermarket electronics, or the dome light or rear hatch cargo light.

It’s just a harbor freight multi meter, nothing too fancy, i believe it only has a 10amp setting. I will definitely check those area for parasitic draw when I get home from work though, I appreciate the input!

50 mA is generally considered parasitic. Keep unplugging fuses until you find your culprit. Leaving the key in will draw more amperage ei: Leaving key in all winter is sure to kill the battery... at least in my car.
I did end up measuring draw on my FC with and without key at some point. It was a measurable difference but I can't remember the exact numbers.

There's a lot of good advice in this thread, once you know how to measure current you simply pull each fuse one-by-one until you find which fuse (or fuses) make the drain stop. Even if you don't understand what gets powered by that fuse, keep good notes and others here might be willing to help walk you through the wiring diagrams.

I once helped someone check for drains 10-15 years ago and the little orange light near the ignition key threw us off the trail because it was drawing current when the doors were open. Try closing the doors while testing.

Yea definitely a lot of good information, and I really appreciate it from everyone. I had to prioritize work and yard work the last few days so I haven’t gotten a chance to mess with it, but I’m going to tonight and hopefully I can find something

Once you've pulled fuses and identified the circuit that has the draw, you can also check relays on that circuit as they can fail or rust up causing a draw.

I had a short on the room fuse circuit and a battery drain problem ever since i owned the car. Turned out the audio relay in the front relay box was corroded inside and was the source to all my problems.

oh good call, I didn’t even think of that! I found my culprit though it’s the 10amp fuse under the kick panel

https://cimg7.ibsrv.net/gimg/www.rx7...da1923baf.jpeg

Also when I was undoing the door sensor (just taking the ground screw out) I heard an actuator type sound, it sounded like it came from between the antenna and door, and my multimeter temporarily went down to 0.00, I have no idea what that was about.

That's progress. You have a few things to check:


https://cimg8.ibsrv.net/gimg/www.rx7...53ba3b5d2b.png

That’s perfect thanks! What’s the pcmt and pcme?

I think it's engine ECU and auto trans ECU at a guess. Typically PCM = Powertrain Control Module.

Dale

SAE standard abbreviations:

PCME = power control module (engine) [formerly ECU]
PCMT = power control module (transmission) [formerly EC-AT control unit]

that makes sense thank you! So to test and see what’s causing the drain, I would just “unplug” the corresponding piece? Like take the radio out, test for a draw, remove cluster, test for a draw, ect?

Cluster? Have you already tested and eliminated all the easier things -- glove box light, dome/door lights, rear hatch light, and then the power antenna and your aftermarket radio? (if your car is pre-'94, there was a Mazda bulletin about faulty glove box light switches that wouldn't turn off.)

oh no I haven’t, I was just giving examples, it’s a 92, I just took the aftermarket radio out and it didn’t make a difference, the rear hatch light doesn’t turn on, to rules out causes I just remove the bulb right?

also found out I had a stripped antenna wire being held into the antenna port with a drywall screw, that was new to me lol

and idk if I’m just dumb and not seeing it, but I don’t even see a glove box light. It may have been removed prior to me?