Parasitic draw on battery

  1. My model of MX-5 is: 2007 NC Sport 2.0
  2. I’m based near: West Wales
  3. I’m looking for technical help or recommendations on: Battery drain

Apologies - topic was created before I had a chance to explain the issue in depth!

I have an issue with my MX5 NC Sport 2.0L with the battery becoming completely discharged after 4/5 days if the vehicle is not used. The battery is new and 100% charged. The vehicle has previously suffered water ingress via both the rear drains and the front scuttle panel and I believed that the source of the battery drain was the Bose head unit / power amp. I have taken it to an auto electrician to verify the cause before embarking on upgrading the infotainment system and they have called to say that the source of the power drain is, in fact, the instrument cluster. They have said that to investigate precisely what within the instrument cluster is causing the drain would be prohibitively time consuming and costly and have suggested replacing the instrument cluster with a used unit.

Is a failure of the instrument cluster a known phenomenon? All instruments, lights, warning lights, gauges are working fine.

The garage is recommending replacing the instrument with a used unit from an identical vehicle (which obviously would have no guarantee) but have indicated that the data from the original unit would need to be downloaded and coded onto the replacement to preserve mileage, etc.

The overall cost, including the purchase of the second hand instrument cluster, specialist coding of the replacement and swapping out is estimated in the region of £500/600, and whilst the garage is confident that this will solve the problem they cannot offer a complete guarantee.

I would greatly welcome the thoughts and observations of the community (apologies - whilst I am generally ok with mechanics, electrics are a “dark art” to me!!!)

Cheers! Richard

A simple check, did you check or have you had your battery checked? These battery problems always crop up in winter, a battery not holding a charge may tell you on the charger it’s 100% charged when not. I’ve had two batteries one more recently where it says fully charged but basically they needed replacing.

Mick, he said that the battery is new and 100% charged.

Ahh, missed the new bit.:+1:

4/5 days is a bit quick, what is the actual drain in amps? Does the drain disappear if the “room” fuse (fuse 5) in the engine bay fuse box? or the meter fuse (fuse 3) in the kick panel fuse box are removed? Have you made sure the boot light goes out when the boot is closed? (use a smart phone set to video in the boot when the lid is shut).

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Being a sport - I am guessing it has the BOSE stereo ?

I have seen on a few forums where the Bose amp can drain the battery quite quickly when it is starting to fail.

Try pulling the 20amp fuse that feeds the amp.
You won’t have stereo sound whilst the fuse is out but it will tell you if the amp is the drain on the battery.

Thanks - it does indeed have the Bose system with the separate amp. This was one of my prime suspect for the source of the battery drain having read several articles like you and recognising that, given its location, it would have been vulnerable when the rear drains became blocked. Auto electrician, however, is adamant that having checked all components, the instrument cluster is the culprit. Replacement used instrument cluster now being ordered which will then be sent to be “cloned” with the data from the original - fingers firmly crossed!

I said in another thread, check the alternator. Alternator failure (diodes) can lead it to drain a battery, without warning lights.