Battery drain

[JTPSL500]

I have a 95 sl500 and If I dont start it for 2 days, my battery is drained. There are no lights on the dash showing or interior lights left on for that matter. Any hints on where I should look first?

[tecqboy]

This problem seems to happen frequently on the 129's. So, try doing a forum search. But, in my particular case ( 91 SL300 ), the lamp in the trunk would sometimes stay on ( bad switch ). Of course, you could never see it. Some other issues are the aux water pump / mono valve running too long after shut down, vacuum locking system causing the pump in the trunk to run, and alarm system. We are assuming of course that you have a good battery and charging system and that your cables are connected well and in good condition. If you have an amp meter, you can try measuring how much current is drawn with the key off. It should be well under 1/2 amp.

[cbdo]

Slow-and-painful-but-effective way of narrowing it down is to wire in an ammeter, then pull fuses one by one until the abnormal drain is squelched; that'll at least tell you what circuit is involved.

[tec01]

JTPSL500: My 1990 500SL has did the same thing a couple of times in the last two years and it seemed to be caused by the power antenna. When my battery is not quite fully charged and I shut the key off the power antenna does not rertract all the way and it will kill the battery. Try unplugging the power antenna in the truck and see if it still kills the battery. It's a long shot but easy to ckeck. Good Luck!

[t walgamuth]

Originally Posted by tecqboy

This problem seems to happen frequently on the 129's. So, try doing a forum search. But, in my particular case ( 91 SL300 ), the lamp in the trunk would sometimes stay on ( bad switch ). Of course, you could never see it. Some other issues are the aux water pump / mono valve running too long after shut down, vacuum locking system causing the pump in the trunk to run, and alarm system. We are assuming of course that you have a good battery and charging system and that your cables are connected well and in good condition. If you have an amp meter, you can try measuring how much current is drawn with the key off. It should be well under 1/2 amp.

i had this on my 84 sec. the switch on it wasnt closing all the way. i think the edge of my trunk edge protector may be broken off making too much space to fill with the switch plunger. we removed the bulb.

tom w

[JTPSL500]

Tecqboy was right, (thanks Tecqboy) took my cell phone hit video capture, placed it in the trunk and shut it for 10 sec. playing back the video noticed the light was staying on. The trunk light switch was off track. Thanks for all the help.......

JTPSL500