Current drain + dash warning lamps

[hotrodder]

Hey all,

A few days ago i bought a well specced '93 320te. Plenty of minor faults as you'd expect on a cheap, complex, 15 year old car but all the important bits checked out during viewing/test drive. Looks to have been well looked after for most of it's life (lots of history etc), performed faultlessly on an extended test drive and didn't miss a beat on the 120 mile journey back which also included a couple of lengthy traffic jams. Right to the point...

Stopped off close to home to pick up some food. When i restarted the car all the dash warning lights stayed lit for a few seconds after the engine fired (hmmm). Early evening the next day i go out to the car and discover the battery's flat. Assuming i missed a courtesy light or something i swap out the battery with a spare only to discover that there was nothing left on and i now have no engine warning lamps with the ignition on- just parking brake, ABS and SRS lights. Bugger

None of that explained draining the battery so i checked with an ammeter and have a 2.5A drain with everything off. Pulled fuses one by one, no change. Engine still starts and runs fine, voltmeter across the battery showing 12.5V so i have a charging issue too- alternator looks to have been recently replaced (not that that's probative) but it must have been charging or i would have never have got the car home

Today i've delved deeper. Had half the dash apart to find the (non functioning) alarm and disconnect it. No change and the engine still runs with alarm disconnected- wasn't sure if it immobilised too

When inspecting the car it was obvious that the engine loom has had some work- section to the coils and the MAF (from the appearance of the loom covering this wasn't recent work to 'patch up and knock on'). Couldn't really start delving into that when viewing so i assumed it was from remedial work due to the brittle insulation issues. Had a closer look today and yes i've got some rewiring to do

When connecting the battery you can hear a relay pull in (again everything switched off) which seemed odd. Removing said relay doesn't effect the current drain

Common sense is telling me that the dash and current drain are connected but i can't see how. Hopefully it's a case can't see the woods for the trees.

Anyone come across symptoms like these? AFAIK engine loom issues usually manifest as misfires from ignition shorts to ground (initially at least!) but i admit i didn't research this thoroughly as until i registered here i was under the impression that this problem was more prevelant in hotter climates than the UK

 

[Dieselman]

It sounds like the OVP relay. It's there to protect against reverse polarity and excess voltage.
It's near the battery with a red top and a fuse on it.

 

[hotrodder]

Thanks for quick response Diesel,

You'll have to excuse my denseness here (modern cars electrics aren't really my forte)... are you suggesting the relay is causing all the symptoms or is just related to the lack of charging?

 

[Dieselman]

I suspect at is the relay you hear snapping in and may cause problems with dash lights, such as the SRS light.

 

[hotrodder]

The relay that's switching upon conecting the battery is in the main relay box on offside. It's not fused and unfortunatly is not labelled. Nothing to hand that suggests what it switches, didn't bother deducing it's function for myself (yet) as it seemed to be a symptom rather than a cause- why would it be switching with everything on the car switched off? Does it's thing even with the airbag ecu disconnected

SRS light is functioning normally (as are ABS and parking brake), the rest of the warning lamps (charge, oil, coolant etc) are absent

 

[bolide]

How are you measuring the current drain? Does it start when you connect the battery or when the ignition is switched on? If the latter, at what key position does it start?

You will need a circuit diagram to diagnose this and accurate ones are hard to find

I'd start by looking at jammed window switches, puddle lights, seat motors & possibly the tailgate motor & sunroof motor. I'd also be suspicious of the ignition switch

If something's drawing 2.5 amps it's dissipating 30-odd Watts so will be getting quite hot

Nick Froome
www.w124.co.uk

 

[hotrodder]

Hey Nick,
Current drain is present as soon as the battery is connected. Not checked with ignition on- from your wording... are the ignition switches on these models known to 'bug out'? Will check drain in all ignition positions tomorrow

Puddle lights etc, checked all those out upon discovering the flat battery as (until i measured the drain) they seemed the most likely culprit

Am measuring current drain with an ammeter between the battery and it's lead- meter is accurate enough to detect the change in draw that occurs when courtesy lights are switched on

I've had all the fuses out one at a time while measuring the current drain- no change. Only did this with ignition off but if the culprit were only powered with ignition on then i wouldn't have a drain with ignition off.

Tailgate motor... ASSumed i'd hear it if that were the culpret

The 'minor' faults the car has (some the owner told me about, some i found)...

Front nearside window not working- switch operates the motor fine, glass doesn't move. I ASSume it's a simple mechanical fix
Interior/demister fan not working. Doubt i'll enjoy fixing that!
Aircon not working
A couple of dash lights out

 

[hotrodder]

Right, stopped ignoring the basics today and disconnected the 'new' alternator. Doing that fixed the current drain so i'll take it to a mate of a mates to be tested and see what the score is

That leaves the dash lights. Anyonyone know if there's an external/extra fuse for these hidden in the dash/behind the binnicle? Am wondering if these staying lit for a little too long after starting the engine was a 'spike' from the alternator as it died or something...

 

[jaymanek]

No there isnt any fuses specifically for certain lights on a cluster..

I would look at the actual ignition switch... that may have bad contacts in it.

 

[grober]

If removing the alternator cures the problem chances are the rectifier/control pack is faulty . If some of the diodes are fried then this can cause a high current drain to earth . There is also an earthing point on the bulkhead behind the instrument cluster which can have a poor connection-worth checking out.