FredR

I have two batteries for my 928 one is about 2 years old that I have been running and one is a relatively new item that I keep as a standby. Over here batteries typically last about 2 years - rarely more no matter the make. During the hot season I typically run the 928 at weekends and thus the car sits in my garage for 5 days before being fired up again. Last weekend I went to run the car and the battery was flat- figured at its age it had expired. N issue put the newer battery in, it fired up and ran no problem. Yesterday I went to run the thing- the battery was flat. Measured the voltage on both of the batteries- the newer one showed 8 volts, the older one about 7 volts- hmmm!

I have a modern smart charger but smart as it is, the internal programming told it the battery was a 6 volt item and could not do much about that so have taken the batteries for a full boost charge at a local shop. Now I have to analyse why it is draining over a period of 5 days. After removing the battery I tried to take some resistance to earth reading from the positive terminal. At lower scale ohm values up to 2k ohms it did not read anything. At 20k ohms scale it then read about 10 ohms. Put the digital meter on one of my other cars with the earth strap disconnected.and at 20k ohms scale no reading measured.

Much appreciate if any of you chaps who are more into electrical problems can advise what if anything I can read into this.

I installed a new engine harness that built a few months ago- has been working well and the only other item of note is that the insert on the rear hatch mostly fell to pieces a couple of weeks ago and pending a replacement the hatch now rattles a bit- can this leave anything engergised and thus bleed amps to earth?

Beyond that, assuming my battery charges up OK I will do a check of current to earth when I get them back. If the battery goes flat in a maximum of 120 hours that suggests a drain in the region of at least 500 mA.

I have read just about everything thread on the subject matter previously in anticipation of having to deal with the type of problem sooner or latter. Nonetheless suggestions as to best analytical approach also appreciated as electrical issues are not my favourite problems to solve..

Majestic Moose

Set up your volt meter to measure amps. There should be three ports to plug in your probes. Move one to the port that says fused at 10A between the ports then turn the dial to the 10A setting as well.

Turn off all interior lights first. This is easier with a helper, lift the ground strap off the battery and touch one probe to the negative terminal on the battery and the other to the ground strap. Now any electrical load in the car is flowing through the volt meter and will be displayed. See how much of a drain there really is.

Step one in this case if you consider the engine harness as a recent variable, is to determine if the fault is inside or outside of the car.

Switch positions with your helper or have them undo the jump post connection and see if there is a large change. If yes, the problem is inside the car.

Remake the jump post connection and have your helper remove fuses one by one and see if there is a one that causes a big drop in the drain to an acceptable level. This will pinpoint the problem component.

If no, then the engine harness having been recently replaced is a suspect here, check for any wires rubbing through the insulation against the engine. Inspect the positive cable starting at the battery and running to the engine harness under the chassis for damage. There is also an unfused cable going to the ABS pump to inspect.

dr bob

Majestic Moose

How could I forget about the jump post?! Though unplugging the 14 pin as well may further isolate the problem?

Alan

All this mention of the 14 pin connector is odd. It is not relevant much at all - and certainly not to inside/outside the car. Don't mess with the 14 pin connector - mostly bad will come from it (something may fall apart!), and it won't tell you anything.

Do measure in series with the ground strap as noted - however: Drive the car for a bit - stop, key off & out. Start with the ground strap connected and the multi-meter in 10A mode connected to the battery -Ve and a different ground point, then disconnect the battery ground strap and see what reading you get? [keep the interior lights off (NOT just turned off) - easiest is to pull off the brown/white wire from the hatch switch (and if needed tape the door pin switches)].

If you measure <200mA - reconnect the ground strap and select 200mA mode then disconnect the ground strap again and see what the actual measurements is? if you don't get <200mA check the interior lights again (door end lights) and if not that start pulling fuses 1 at a time to identify the culprit. Note not everything is fused - but this is a start. Report what you see..

Unless you keep the battery in circuit you will miss currents that depend on initiation when running, and maintenance after running...

Alan

The Forgotten On

It also doesn't hurt to feel each of the relays after the car has sat for a while to see if it is warm. If it is, there is a current leak in that circuit which could be a short, a failed, relay or something else.

FredR

Gents,

Thanks for the inputs to date. My batteries charged up OK so for sure I a leaking juice somewhere. I have plenty of experience checking earth leakage previously so no problem with that one other than the damm temps that are stinking hot and humid at the moment even in my garage- must get an a/c fitted in there!

Did anyone have any thoughts about the hatch latch insert failure possibly contributing somehow [unlikely but?] or the resistance to earth via the positive cable? I will fit a battery this afternoon and possibly do the current check after running the motor up.

Mrmerlin

disconnect the hatch pin connector or replace the collar then test the battery as Alan has suggested.

I would drive the car then park it,
shoot the relays with an IR gun then close the door and come back in 20 mins and see what relay is still hot

NOTE I had a similar issue with my 88 and it was the blower relay that was sticking on after the car was shut off.
I also found the X relay was sticking on,
I replaced both relays and operation has been good.

NOTE relays being subject to low cranking volts can be damaged,
as this can cause the relay to not fully close this makes the contacts arc over time,
even with a good power supply the relay performance will degrade

jpitman2

I find this sort of meter very easy to use if you have blade fuses....get one to suit your fuse size. Sadly not usable on my model.
https://www.ebay.com.au/itm/Car-Batt...MAAOSwKrxUZ24o
jp 83 Euro S AT 57k

FredR

Those are neat!

FredR

Stan,

Not sure I understand what you are suggesting.

At the moment I have a difficult choice to make- go and work on the car in 40C heat with RH about 60% or watch the British F1 grand prix from Silverstone- a difficult choice- decided on the F1!

Will have a go at the 928 first thing tomorrow morning before the sun frazzes everything again.

Koenig-Specials 928

Mine was a PW relay. It was so hot after the car was shut off for an hour I needed a pliers to remove them.
I was surprised it did not ignite.

Wow, this thread is a keeper. It reads like a tutorial with input from the people I trust the most on this site Stan, Dr Bob and Alan
Thanks gents!

dr bob

In the US, Harbor Freight stores sell a couple versions of this handy meter, different for different fuse types. I added a fuseholder with pigtails and alligator clips to the package, so I can plug the meter into the fuseholder and use the pigtails to test in places where there isn't a fuse local. There's a 30A-capable version that reads down to LSD=tens of milliamps, so while not good for finding the last few, it will certainly get you close enough to go after the measurements with a more precision instrument. If the smoke leaks out I'm out less than $20. Plus there is a separate fuse socket that should protect the circuit if not the meter.

FredR

Small update:

Took a look at the thing this morning and found a couple of issues. I normally leave the door lights in the switched off position. The passenger door light switched on ok but not the driver's side. Maybe it has a blown bulb or maybe I have done something daft when I had the door card off a while ago and either the power supply or the earth is not connected. I also noticed that the light above the rear seats is not functioning - it does not seem to have switch. I suspect it has been like that for a long time- never noticed. Having read the thread on the hatch release with a system description by Alan, I tried to operate the hatch release **** that I have not tried to operate for a long time- it did not work- did not even feel like the switch was lifting as if it was seized. This reminded me of a leakage incident I had with my late S4 many years ago. Turned out the problem was being caused by a short in the wiring somewhere in or around the hatch- which I came to understand is quite a common issue - hmmm!

After half an hour in the garage I was leaking water faster than a knackered air stewardess so called a time out. Will try to take some amp leakage measurements later today all being well assuming I can figure out how/where to hard connect the multimeter prongs prior to undoing the earth strap. Will also test the 1 amp fuse [no 26 or whatever]..


.

FredR

Further update after working on the thing this afternoon - lost another chunk of body mass- urrgh!

Measured earth leakage and the meter suggested "zro amps"- did not believe that- checked the 10 amp fuse in my digital meter- it was caput! Better still the 2 amp fuse was not even present- durrgh!

Still, I did a bit more sniffing around - pulled the connector to the release actuator motor [as Stan suggested] - tested the resistance across the pins and the reading was about 4 ohms. I then tested resistance of both pins to earth expecting infinite resistance and got a reading on both pins of about 13 ohms to earth- that to me does not sound right- anyone got any thoughts on that ? I intend to pull the assembly this evening or tomorrow and test the motor.

In the meantime I need to find some suitable fuses for my meter [or some fuse wire].