1982 380SL battery run-down

[300sdToronto]

I just experienced a partially discharged battery on my 380SL (10.5V with the headlights on, insufficient power to turn engine over on a cold morning) and I suspect the alternator is on its way out and charging insufficiently. Battery is less than one year old but I will have it tested. Alernator has 109K miles and a prime candidate for retirement.

Just to set my mind at rest - please can anyone confirm that there is nothing drawing battery power on these cars except the clock when everything is switched off?? They are way too simple, surely for any electronics in permanent standby mode.

So if I put an ammeter on the battery and see a current of more than a few mA then I assume I have a short somewhere??

[mbboy]

Originally Posted by 300sdToronto

Just to set my mind at rest - please can anyone confirm that there is nothing drawing battery power on these cars except the clock when everything is switched off?? They are way too simple, surely for any electronics in permanent standby mode.So if I put an ammeter on the battery and see a current of more than a few mA then I assume I have a short somewhere??

Maybe not. I have heard of batteries being drawn down by the motors in AC/Heater servos failing to go into the park position. Turn the car off and put your ear next to the big, black, plastic cannister with all the vacuum and electrical lines going into it on the passenger-side of the engine compartment just in front of the firewall.

[ctaylor738]

A 1982 would not have the servo. Offhand, I can't think of anything other than the clock.

If you do have a current draw, then test for amps on each fuse to try to isolate the problem.

[coleyjf]

Hi there

One thing I have that drains the battery when everything is "OFF" is the "dealer fitted" remote alarm system - the receiver has to be powered all the time so it can respond to remote activator:

My "Tracker" device (not sure if they are very common in North America) fitted by one of the previous owners. These are well hidden so if there is one you may not know about it.

Cheers

Jim

[300sdToronto]

Thanks. I suspect poor charge from the alternator - not enough to turn the warning light on but bad enough to weaken the battery with short trips at night and so on. Once the battery is charged she starts well even on a cold morning so this is not a grounding or a starter motor issue.

I will test for leakage/drain first, as it looks like a major pita to remove the alternator - much less access than on my 300SD!

[380mark]

Dash clock and stereo draw continuous power.