Hey guys, looking for some assistance/confirmation on my parasitic draw that kills my battery in roughly 24 hours (down to 3-4V). It's not boosted yet but will be soon and you guys have so much knowledge.

92 chassis w/ VVT swap per megathread, stock NA engine besides DIY intake to fit the chassis and running on MS3Pro PnP. Alternator is an internally regulated 100A FD Rx7, no modifications besides the mounting bolt/belt length and enlarging the ring terminal to fit over the post. REMY 14451 (reman) from Rockauto as I could not find an OEM one and I'd heard rather positive reviews. Swap was done last Oct and haven't had issues until now. Voltage looks good while running and shut off unless it sits for a day, then its down to 3-4V.

Testing throughout the past few days:

• I have a spare battery so tried swapping them, both act exactly the same. They will hold charge fine when disconnected from chassis.
• When initially connecting the battery, draw is only .12A w/ multimeter in series (still seems high but not enough to kill it this fast, will try re measuring on 250mA setting to confirm)
• Key on, DC clamp meter shows about 8A then drops to around 3A with key off (I know these aren't very accurate, just didn't want to fry multimeter 10A max)
• Disconnect + terminal and add multimeter in series shows 2.8A draw w/ key still in off position.
• If you disconnect the battery, and tap the brake pedal to drain any residual/capacitance, then reconnect the battery it will not be dead the next day
• Confirmed with multimeter in series that after disconnect, tap brake, reconnect the draw is now back to .12A until you key on/off again.

So my rather limited electronics knowledge leads me to think a relay is sticking or something and I start pulling fuses, relays and connectors to try and find what.

• Beginning in engine bay, pulling main 80A fuse removes the large draw and brings down to .12A. Pulling the other fuses in that box have no affect.
• Pulling relays in passenger side have no affect
• Pulling main yellow relay under dash has no affect.

At this point I move to (trying) to read wiring diagrams, hopefully this attachment works.

• moving down flow of the 80A main fuse, I unbolt the + ring terminal from the post on the alternator. Draw goes away.
• Draw does not return if I cycle key on/off if disconnected, if reconnected it does.
• When + terminal connected, unplugging the 2 wire connector from the alternator, draw does not change or go away.

This leads me to think alternator is the culprit. Is this correct or am I missing something. I'm assuming a diode or something is bad, but why does it drain only after key on/off but not just any time battery is connected? Please critique my process and let me know what I'm missing, and roast me for getting a reman "upgrade".

TLDR: parasitic draw of 2.8A until I disconnect main fuse or alternator + terminal. Nothing else I could find had an affect.

 

Your test with the 2.8amp with multimeter in series is the correct way to test a draw. Once the key is off and you see that 2.8amp draw, try removing fuses from the footwell fuse box.. There will be a fuse that drops the amp draw to near 0, that's the circuit you want to focus on. Typically it's an aftermarket radio or alarm. By removing the main fuse, you've cut off battery voltage to the TNS relay, room fuse, stop fuse, ABS, fan relay, air bags, AC fan relay, and ignition switch, so I wouldn't be confident it's the alternator with what you've tested. I've never seen a bad alternator cause a draw, I've only see it cause over or under voltage charging. First time for everything, but that's my $.02.

Stop fuse powers cruise control, horn relay, brake switch with splices to shift lock, cruise, ABS, and ECU, room fuse powers one pin of the ECU, radio(!), interior lights, ignition switch reminder, and another pin on the shift lock actuator.

 

Thanks for the help Curly. I thought removing the alt + terminal isolated it to that rather than rest of car and since 2.8A is pretty large it could make sense. But I've also never seen an alternator fail like that which is why I wanted confirmation before buying a new one. (Might be able to get it warrantied from Rockauto but not confident in that). I'll try repeating the test tonight and pulling the fuses in the footwell, I had avoided it since it's a pain to crawl in and out of that position haha. Maybe I can recruit my wife to watch the multimeter while I stay crammed under there.

Assuming pulling all those fuses has no affect on the draw I would be suspicious of alternator again? I think I have a couple NB alternators laying around so I was thinking about mocking one up to see if the draw does the same thing or not. Obviously not starting it since it's externally regulated, but I assume I would be save to just hook up the power and ground to it.

 

2.8A at 12V is nearly 36W, which should generate noticeable heat.

 

Agreed, it's quite significant which is why I'm still a little suspect of the alternator and wanted to check if it was warm but didn't get a chance to let the chassis cool off and check.

I ended up (accidently) cutting my trans cooler line on my truck while I was cutting some exhaust bolts to replace a gasket last night sooo that has taken priority and miata saved the day for my commute... Will finish diagnosing tonight or tomorrow.

 

Alright still struggling to diagnose this and any input would be appreciated. I'm leading to believe that it may be being drawn through the alternator but the alternator itself isn't the root problem?

Update and correcting a **previously incorrect statement**:

Testing with current internally regulated FD RX7 100A alternator (car drives fine just has parasitic draw)

• @curly Pulling all fuses in fuse box under dash while key is off has no affect on roughly 3A parasitic draw.
• @Ted75zcar It was 90+deg so I couldn't really tell if the alt was generating heat. IR thermometer showed the alt case raising temp by 1 deg over ~5 min but will re check tonight now that its colder.
• Starting with battery disconnected, hook it up, key on, then key off, it continues to draw 3A.
• Unplugging the main fuse or the positive terminal on the alternator, or removing alternator from chassis (ground) will instantly remove the draw.
• Unplugging the alternator 2 pin plug (w/ pos terminal connected) will not change draw from 3A
• Cycling the key on and off with 2 pin plug disconnected (w/ pos terminal connected) continues to draw 3A
• **UNLESS with 2 pin still unplugged I disconnect the battery, tap brakes, reconnect battery, and repeat key on and off again. It now drops from 3A to normal draw.**
• Pulling INJ 30A fuse (wiring diagram shows that connecting to alt 2 pin plug) has no affect on the draw throughout each test, but my rad fan runs when key on. Normal? I assume something with false high temp reading due to no voltage?

Testing hooking up a known good 01 VVT NB2 externally regulated alternator I have. (NA chassis not wired to control it, I didn't start the car ofc)

• All tests act the same, except when unplugging the 2 pin connector the draw goes away without needing to "re set" with a battery disconnect.
• Removing the 30A INJ fuse removes the draw immediately and will draw again as soon as you re insert it.

Can anyone explain the role of the 2 Pin alt connector and what I'm seeing?? I thought on NAs it was just to run that cluster battery light but looks like there's more to it. I'm having trouble seeing from the wiring diagram what it is feeding/being fed by. INJ fuse? 80A fuse from alt? Do the arrows on the wiring diagram show direction of flow (doesn't seem like it)?

Next planned steps:

• Check if alternator getting warm when sitting with draw once I have a chance to get the chassis cool.
• Repeat tests tomorrow hooking up an NA alternator that my buddy is going to bring to the AutoX event lol

 

Just to be clear, you have the multimeter in series with the battery, showing a 3amp draw, and you're removing one fuse at a time in both the engine bay fuse box and dash fuse box, checking the multimeter after each fuse, and the 3amp draw never goes away?

The two pin alternator connector has two purposes, one, it feeds the alternator 12v from the INJ fuse, this is the signal the regulator uses to determine if it needs to charge or not. The other is an output for the charge indicator on the dash.

 

Thanks for the quick input!

Correct, multimeter in series reads about a 2.8 A draw.

I confirmed this matched close enough with my DC clamp meter (2.8A vs 3A) and drops to <.1A when I get the draw removed) I used the DC clamp ammeter to streamline the testing though because I can't switch key on while my multimeter is connected in series as I tried that earlier and blew the 10A fuse in my multimeter because I assume it draws more than 10A for a moment when I first switch on the key, then sits at like 5-8A as FP primes wideband heats etc. but I did turn off my wideband for testing this time.

Correct, the only fuse I can remove that removes the draw immediately with the internally regulated alternator is the Main 80A fuse. All other fuses had no affect besides the 30A INJ fuse with the NB2 externally regulated alternator but that may just be because it's not wired for it to control the alternator. Hopefully can confirm this tomorrow with an NA alternator.

From what you're saying about the 2pin alternator connector it sounds like maybe my alternator is trying to charge when it should not, and therefore drawing on my battery? Diagram looks like the INJ fuse is always hot though so curious how it uses that to determine if it needs to charge.

 

The wideband will only draw about an amp, it's the FP blowing the fuse. Here's a little secret, I don't keep the 10amp fuse in my multimeter, just put a 15amp in, and suddenly you have a 15amp multimeter!

What'd you find with the spare NA alternator?

 

Yeah figured it was the FP since it had already dropped by the time it had primed, I supposed I could have unplugged it. Haha maybe I'll just do that next time, I assumed something on the circuitry couldn't handle more than 10A.

I hooked up the borrowed NA8 alternator during lunch at autox (2 pin connector, pos term and grounded the case) and it acted normally like I would expect. No parasitic draw under same conditions so I'm pretty sure some diodes or something in my FD RX7 alternator failed? I'm going to see if Rockauto will warranty it since its only like 9 months old.

Thanks for your help and I'll update this once it's fixed in case anyone else has this in the future.

 

For anyone reading this in the future, finally swapped in the OEM NA8 alternator last week and no more issues.

Bonus I found out the slightly longer Bando 4PK890 works and has enough adjustment with both the OEM NA8 alternator and the FD RX7 alternator.