Battery drain current
 

Recently I came back from a business trip and could not start up my car in the airport parking lot (I was away 7 days).
The battery was only 6 months old.

After searching on this forum and using procedures suggested by fellow members, I found the battery was drawing 100 mA when the car was off. I took fuse # 2 off, the battery was drawing 3 mA.
Fuse # 2 supplies current to the following circuits: (information from fuse box)

Clock, trunk light, diagnostic, switch-over valve seat back arrester,
roof light front + rear, hazard warning system, automatic antenna,
illuminated vanity mirror, warning monitor, electronic radio

I isolated the problem was not from trunk light, roof (interior) lights, antenna, radio.
I suspect it is the clock, which has not been running for years.
The question I have is: how do you disconnect the clock?

Thank you

David
_______________________
1985 300D Turbo

Your diagnosis is likely correct.

A broken clock can draw an excessive amout of current when it's stalled.

If you remove the instrument cluster, the clock has a single wire attached to a terminal lug. Simply unplug it.

The cluster pulls straight out using two hooks on either side. If you don't have the hooks, it can be pushed forward from underneath and behind.

Hi Brian
Thank you. This afternoon, I took off the cluster and removed the clock terminal wire.
After put everything back, the current draw is about 30 mA with ignation off.
Is that normal?

Thank you

David
___________________
1985 300D Turbo

Considering that the latest high capacity AA size batteries could sustain a draw of 30ma for about 3.5 days, I'd not be too worried about it if thats all thats being used. Seems like it should still be lower though...maybe the radio is using some juice? I thought it was supposed to be like under 10ma when the car was off on our cars....I could be (and probably am) wrong though.

Is there an alarm? If not the only things on a W123 that should draw currant when its off is the clock and radio. Pull the fuse for the radio and see if it drops to zero or darn close to it.

30ma is perfectly normal. The battery will last for 30 days at that discharge rate. Anything below 60ma is fine. If the clock was functioning, you would be about 60ma.