Battery Drain on 116 (LONG - Sorry!)

[TClanton]

Hey Guys,

Having a strange problem with my 80 300SD. No problems starting all winter or spring, then early in summer I went out to drive it and the battery was dead. First thought was that I had left a door open or interior light on, so I charged the battery and it started, no prob. Went out two days later...dead.

The only thing I could think of was a dash rheostat replacement I had my indy do earlier in the spring, but no problems for months. Right after he put the new rheo in, the tach light flickered a couple of times and the radio did the same. Some kind of short from pulling the instrument cluster? It never flickered again, so I don't know if there is any correlation.

Had the car towed to the indy (mentioned the flicker) and he told me the battery was bad. Took the battery for exchange and was told it was fine. My indy is a certified MB guy and has always taken good care of me, so I argued and got a new battery. Put it in, went out a couple of days later....dead battery.

Sent it back to the shop....said the alt wasn't charging at idle. The alt we put in 1 1/2 years ago that had to be rebuilt twice. Out of warranty. Fine. Put in a new Bosch rebuilt alt and brought her home. Two days later....dead battery.

Charged battery again (disconnected when not running...that bracket is a b*&%ch ) and indy says to unplug the servo and see if it is the source of the problem. Otherwise, it might be the glowplug relay.

Left the battery connected tonight with servo unplugged. We'll see what morning brings.

Any ideas? I trust my indy, but I think he's missing something. His business has taken off and I don't know if he's paying attention. Also, anybody know of a thread with some "how-to" on servo replacement? Can't be too difficult!

Thanks!
Terry

[wbain5280]

First of all, don't appologize for a long post with complete info.

You might want to check the trunk light switch. Since the trunk is closed and little to no light escapes, you can't tell if it's on. Open the trunk, make sure the light is on then push the light switch plunger in. Light off?

The next thing to do is to use, or get, a voltmeter with an ampere setting. With owners manual in hand, remove each fuse and measure the current. Start with a higher current and work lower. Test each fuse in order looking for higher than normal current flow, normal meaning no current or a few milliamps.

The owners manual will show what each fuse powers .

[Hit Man X]

Bad voltage regulators do the strangest things! It took my buddy and I about two weeks to go back to that after going through two alts on his '72 Sedan de Ville. Granted it was a firewall mounted external reg...

[boneheaddoctor]

My W116 last year has a simmular problem it woudl every few months decide to drain the battery...at random intervals...

Turned out to be a flakey regulator.

[oxymoron]

my money's on a servo that won't park

[mr sweattypits]

I have been having an almost identical problem... about the same time the radio started cutting in and out the tach jumped a few times (first time i have seen it move) the battery started dying. did a key-out volt reading and its the #1 fuse. since my fuse card is MIA and i started pulling lights
and no bueno. i thinks its behind the dash. i will hopefully find out today. definitly remove the negitive connection on the battery with the key out (test light is ok but voltmeter is better) bride the circut with your tester and start pulling fuses until the voltage drops below at least 9volts. should be about 5 volts (for the clock) somewhere i read in here about a soldering fix behind the dash. good luck and i will get back with my results (hopefully)

[TClanton]

Checked it this morning and 12 hours since I unplugged the servo, still got a full charge. Hadn't thought about the voltage regulator.....

I'll keep monitoring and posting progress!

Thanks,
Terry

[boneheaddoctor]

keep an eye on it and let us know.....

[oxymoron]

servo replacement is one screw on the vacuum manifold, two screws (SAE!) on the bracket, 4 hose clamps and the electric connector.

get a metal one if you can. the last new plastic one i bought lasted 2 years and they are sick expensive from the dealer if you can even find one.

Robert at EEC has one on eBay almost all the time.

or Fastlane now sells the electronic replacement.

I went thru a couple of batteries until the servo thing got solved.

When my voltage regulator went out, the first signs of it going bad were a tach that was jumpy

[boneheaddoctor]

Originally Posted by oxymoron

servo replacement is one screw on the vacuum manifold, two screws (SAE!) on the bracket, 4 hose clamps and the electric connector.

get a metal one if you can. the last new plastic one i bought lasted 2 years and they are sick expensive from the dealer if you can even find one.

Robert at EEC has one on eBay almost all the time.

or Fastlane now sells the electronic replacement.

I went thru a couple of batteries until the servo thing got solved.

When my voltage regulator went out, the first signs of it going bad were a tach that was jumpy

My tach never got jumpy....it woul discharge for no good reason...I finally caught it one time when it desided to overcharge...but most of the time it worked perfectly.

the point being a bad regulator can have a lot of symptoms.

If it does turn out to be the Servo check your servo amp behind the glove box...replace it it it appears to be burnt.