E39 530i touring - Nav fuse stray voltage on earth side - battery drain

[ruston]

Probably your multimeter, an ECU should shut down above 18 volts to protect itself.
The ECU has upper and lower operating voltage limits.

 

[DPG]

Hi,
I have not had the battery tested, but it has now been flattened a few times because of the draw, it was a year old and 100Ah. I put a new one in it yesterday, eaxacly the same as the old one, so I can rule it out as an issue. Voltage goes up quite high when the engine is running so it is definitely charging.
I'm convinced I have found the piece of kit causing the problem, although I dont actually know whats wrong with it. Presumably it could be a wiring porblem as well rather than the equipment itself.

That draw was OK for about a year (when I put the last battery in) and obviusly killed it over that time period as I only drove the car every two weeks. But when it did get driven it was two long journeys of 70 miles each over the course of the day, so it was getting charged properly each time.

I suppose I should try another Nav unit in there and if the problem remains its in the wiring, and if the problem goes, it was a problem with the original unit.

Just been out and tested a few things with the multimeter and some strange things going on.

Brand new battery car off: 18.7 V
New battery engine on tickover: 20.7 V
1500 rpm: 21.9 V
2200 rpm: 22.1 V
3000rpm: 22.3 V

So I think voltage regulator is broken, But

Old 'flat' battery: 18.8 V
So is the multimeter knackered??

The easiest way to prove your multimeter is reading correctly is to try another one. Don't run your car until you know that the charge voltage is correct as you will likely damage things.

 

[static zap]

Brand new battery car off: 18.7 V
New battery engine on tickover: 20.7 V

Been there with a DMM reading too high.
If you can find.
A few 1 inch fresh lithium cells 3-3.2 Volts each .
a fresh 9V battery never much more than 9.6 - 10V NEW
.or an old USB cable((plug into Charger (red/black)) ..4.8-5.3V
...
Side light bulbs will all probably look all silvered (black on glass)
if have really over volted things.