Any good auto sparks here?

[hotrodder]

Hey all,

A few days ago i bought a '93 Mercedes 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 100+ mile journey back which included 'spirited' driving and 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. Couldn't really start delving into that when viewing so i ASSumed it was from remedial work due to the brittle insulation issues these cars are known to suffer from. Had a closer look today and yes i've got some rewiring to do as the previous 'work' was more of an inspection and cover up than repair- it's not recent work though

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 (especially as i'm not particullarly clued up on modern car electrics)...

Just joined a Mercedes forum (local knowledge and all that) but any ideas?

 

[shenion]

Try disconnecting the alternator. If the diodes are going bad, they can drain the batt.

Look at the main lead from the batt to look for power leads to devices always powered that don't run through the fuse box (some AC items, ABS, suspension systems.) Theys are usully protected by fusible links. Either there will be some sort of terminal block or they will use one of the terminals on the solenoid. Disconnect these one by one and see if the current draw stops.

 

[hotrodder]

Cheers Shenion,

I had planned to jack up 'Christine' and look at the alternator and starter motor today and sure enough disconnecting the (obviously recently replaced) alternator fixed the current drain. I'll drop that off at a mate of a mates to be tested tomorrow. Being a 'new' alternator i'd stupidly considered it unlikely to be the cause.

Just the dash lights to explain now...

 

[Highway_Star]

Sometimes you can replace the diode pack. I did this on my Range Rover a few years back, the diode pack was £30 IIRC from the Prince of Darkness.

Bizzarely enough, when it went west on me, the charge light came on with the ignition off, but went out with the engine running. It wasn't charging however.

 

[hotrodder]

Highway,
Whenever an alternator has died on me before the charge light has behaved as you described- on or at least faintly glowing with ignition off, nothing else effected. When this one went i lost all the engine warning lamps and as the (bosch) alternator was obviously recently replaced i stupidly didn't check to see if it was charging before looking elswhere

Got the alternator back yesterday- diode pack and voltage regulator had died. Just refitted it and the dashboard is alive again too, only thing i can think of is that the engine check lights get their supply via the alternator/charge light circuit.