Slow Battery Drain

[MG_JDS]

I recently purchased a 96 MGF. I have had a slow battery drain, which I originally thought was the old battery and cold weather (lasts about 3 weeks) New battery is exactly the same, no change, alternator is charging fine and can supply necessary current to feed lights and charge battery whilst running at low revs. Everything checks out on the car. Battery drain after engine is switched off is approx. 500mA for around 10 minutes, then when MEMs shuts down, drain drops down to 70/80mA. Which I still believe is too high, hence battery drain. After further investigation I found that if Fuse 12 (passenger compartment) is removed, battery drain drops from 70mA down to 20mA (this now looks about right I think). From reviewing schematics, Fuse 12 feeds , interior lamps, dash clock, ignition ring lamp, boot and bonnet lamps, radio and diagnostic socket. Now I have disconnected all of the bulbs and circuits from what is shown in the schematics, and the battery drain has dropped to around 57mA. But what I cannot understand is why this has not dropped to 20mA, as when the fuse is removed? The only part I haven't disconnected is the diagnostic socket, but this would appear 12V is run to this and it is not used to supply any circuit. Does anyone know if Fuse 12 has something else connected, which is not documented or if there is anything else worth checking? I know the MEMS, purge valve has no effect nor does ABS, took these off just as test given the diagnostic socket association - but no difference. With fuse 12 removed engine runs as expected, all other circuits would appear functional - so I am at a loss of what else is connected to this Fuse 12 circuit - any ideas would be welcome!

[talkingcars]

Hi and welcome to the forum.

It sounds like you have an idea of what you are doing.

A common fail point is the wiring into the boot lid by the hinge.
Is the boot light working properly?
Strip the insulation back and check for damage.

Another avenue of investigation is the alarm system, does the drain change if the alarm is set?

James

[MG_JDS]

Hi James,

Thanks for the reply.
Having the alarm on or off makes no difference to the current consumed, it is pretty constant armed or un-armed.
Have seen the boot wiring as an issue on previous forums, my boot light does work OK, so wasn't something I have really looked into, but will certainly take another look.
My only other thought is somebody has added to wiring over the years, but there is nothing obvious.
Cheers.

[Helsbyman]

Hi mg_jds can not add anything to the above advise. See you are in the n/w, We have a meet on the 4th fri of the month in Neston at the Hinderton arms if you are interested

[MG_JDS]

Problem solved - found this buried in the rear wing after taking the boot liner out! (GPS tracker????)
This was the current drain I was looking for! Thanks to James for highlighting the boot wiring, after stripping back the boot loom wiring on the hinge, found the purple cable feeding the boot light had been spliced and taken through to this device!

[talkingcars]

Good news.

I stripped my beloved ZS180 of 5 years last year, I thought I knew every inch of that car, I wasn't expecting to find a tracker in the boot.