Is my alarm aftermarket?

Technical Area Electrics & ICE
1
  1. My model of MX-5 is: 2005 NC launch edition
  2. I’m based near: Scotland
  3. I’m looking for technical help or recommendations on: Alarm and battery

I’ve been having some issues with the battery recently (possibly since i got the vehicle tbh), and after fully charging it on a smart charger 2 days ago I awoke today to find that the battery is completely dead again.

When accessing the car the alarm started to go off. Its a beeping coming from the boot, not using the horn. It’s not that loud tbh and it persists despite disconnecting the battery. I can’t get it to stop.

Is this alarm aftermarket, or OEM do you think?

I have to leave for a couple of days right now, but if it’s aftermarket then it’s getting ripped out as soon as I return and I’ll test the draw on the battery both before and after to see what’s up.

Hard to say how old the battery is, but it’s not the original i don’t think. It’s a Yuasa 5000. Certainly it threw no issues on the smart charger and completed a full 24hour cycle.

Sorry for the waffle, in a rush to leave and wanted to get something written before I did!

2

Completely off the cuff thought but do you have rear parking sensors fitted ?
if yes - could they be live all the time rather than just when reverse is selected ?

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3

That’s a good shout but no, there are no parking sensors on the vehicle!

4

The alarm sounds like it’s a factory fit system. It has a battery back is the sounder up so will sound if the lead acid battery is disconnected.

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Hmm, so ill go back to the drawing board once I get the battery changed again and see if I can measure the draw on it.

Got to say it’s a pretty poor alarm for a factory system. You can’t hear it more than a few meters from the vehicle!

6

Hmm, any hidden lights left on?

I noticed the door-open warning light seemed to be on all the time while I did the cavity waxing, which needed a door open, so I left it on the smart charger while working on it.

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7

Not that I can see.

After charging the battery again I’ve ran a multi-meter over it and observed the following:

Engine not running 12.5V
Engine running 14.3V

Seems like both the battery and alternator are working?

Draw with engine off and car locked after 10 mins: 0.08-0.10A

Is this considered too much draw on the battery?

8

Yes, too much. 25mA to 40mA is more normal. My NC was 32mA last time I checked.

But always check this half an hour after switching off, when it has finished doing its security housekeeping.

Edit.

Thinking about this for the last hour I remember two other battery drains I’ve come across on various cars.

Most often the leak was in the alternator, with carbon dust from the brushes providing a path across the insulation in the rectifier stack. Sometimes a blast with a good airline will fix this, but more often the baking effect of passing the current means it needs to be washed off with a stiff paintbrush and the usual solvents, like hot water and a final squirt of Isopropanol.

A couple of times it was the radio, once because the permanent live and switched-live wires were swapped, and once because it was a cheap and nasty duff radio.

I’m sure others will have found more interesting oddities siphoning away hard earned electrons.

But nothing beats a methodical search puling fuses (only one at a time), until the dark current suddenly drops in a big dip.

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9

The dash cam on my daily would drain the battery if the car was stood for a few weeks.

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10

Does the car have BOSE stereo ?
Have seen some reports of faulty Bose amps drawing current all the time.

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11

It’ doesn’t have a BoSE head unit, it’s got an aftermarket one with ■■■■ radio reception! I’ve not had a chance to start eliminating things for the parasitic draw yet, but that’s a prime candidate!

12

Appreciate the detailed reply! Yeah that’s the plan. We’ve got quite a bit on just now, but as soon as I get a free afternoon that’s what I’ll be doing.