Gremlins under the hood

[larryled]

Here‘s a new one for you!  New, because I have never come across one like this in all my 60+ years of owning a Benz, nor do I think it has commonly occurred to others.  The first time something odd happened in my 66 250SE/C was in July while driving to the GWS Picnic.  Coming to a stop in Alexandria the car abruptly died.  It took more than normal time to restart but it did.  It happened again a short distance later while stopped, and the restart again took longer than it usually takes.  All normal the rest of the Trip going and returning home.  This did not seem to be fuel starvation because the shutdown was very quick, almost instantaneous, not like fuel interruption which would take a bit longer to wind down.  Next, two weeks ago while driving to the Rockville Show it did the very same thing in the Middle of a busy intersection, lot of horns!  Took  longer to restart but it did.  On the way home that didn‘t happen but my windshield wipers came on and I couldn‘t turn them off.  They repeatedly did this two or three times and then stopped without any input from me, and I could not shut them off!  I was following a friend whom I called to see if he noticed that, he did, and added that my parking and running lights were  also blinking and all went out except the right parking light.  (European Lights) I confirmed this when I got home, and curiously looked at the fuse box.  # 8 fuse, which controls the lights but not the windshield wipers, was almost totally disintegrated, half the fuse was totally gone and the contact at the fuse was noticeably burned.   I‘ve looked closely at the wiring harness under the hood and no evidence of anything unusual.  I have not looked under the Dash yet.  Obviously I would appreciate any input, and possible answers. Larry

[wjsvb ✝︎]

Check your grounds.  Good luck!

[Mike Hughes]

Ditto on check your grounds.

Some loads have both a "natural" ground simply because they are secured to the engine/body/chassis, yet the manufacturer will insure proper functionality by also including a ground wire for that load in the wiring harness.  Sometimes ground wires from multiple loads come together on one ring or more terminal rings that are then secured to the body/chassis at a single point.  If the screw/bolt securing those terminal rings comes loose all of those loads may still be connected to each other through their ground wires.  As an example, turning on the headlamps can send voltage through the headlamps and then through one or more of the other loads that has a natural ground, such as a horn or a wiper motor or a brake light.

I found this out the hard way many years ago when replacing the radio in my sister's MGB-GT.  The horn was mute, the parking lamps and headlamps wouldn't turn on at all and the electric overdrive wouldn't work.  However, flashing the high beams with the turn signal stalk would also blow the horn.  Then she discovered that when she turned on the parking lamps or headlamps in 4th gear the electric overdrive would engage.  I had undone the common ground terminal ring behind the radio to move the wires out of the way so that I could remove the old radio from behind the dash, and forgotten to hook it back up again after the new radio was installed.  My busted knuckles were even more busted by the time I finally had everything back together again!

[Benz Dr.]

Ditto on check your grounds.

Some loads have both a "natural" ground simply because they are secured to the engine/body/chassis, yet the manufacturer will insure proper functionality by also including a ground wire for that load in the wiring harness.  Sometimes ground wires from multiple loads come together on one ring or more terminal rings that are then secured to the body/chassis at a single point.  If the screw/bolt securing those terminal rings comes loose all of those loads may still be connected to each other through their ground wires.  As an example, turning on the headlamps can send voltage through the headlamps and then through one or more of the other loads that has a natural ground, such as a horn or a wiper motor or a brake light.

I found this out the hard way many years ago when replacing the radio in my sister's MGB-GT.  The horn was mute, the parking lamps and headlamps wouldn't turn on at all and the electric overdrive wouldn't work.  However, flashing the high beams with the turn signal stalk would also blow the horn.  Then she discovered that when she turned on the parking lamps or headlamps in 4th gear the electric overdrive would engage.  I had undone the common ground terminal ring behind the radio to move the wires out of the way so that I could remove the old radio from behind the dash, and forgotten to hook it back up again after the new radio was installed.  My busted knuckles were even more busted by the time I finally had everything back together again!

Yeah, but that's an English car, so it doesn't count.

[ejboyd5]

Perhaps it is time to clean the contacts and replace all the fuses with new ones.

[Mike Hughes]

Yeah, but that's an English car, so it doesn't count.

Oh, surely you have turned wrenches on some "off brand" vehicles at one time or another?  Regardless of vehicle origin I think that experience gained informs how one approaches future problems, don't you?  ;^)

[Benz Dr.]

Oh, surely you have turned wrenches on some "off brand" vehicles at one time or another?  Regardless of vehicle origin I think that experience gained informs how one approaches future problems, don't you?  ;^)

I worked on a couple of Audi sedans back in the 70's and a Volvo once. Never really worked on much else besides MB cars.  Oh, I had a Mini Cooper race car for a while. Almost rolled it one day while having fun on my side road so I decided to get rid of it before something really bad happened - like getting caught with no license or insurance. I was definitely a bigger risk taker 40 years ago.

[Mike Hughes]

Getting back to Larry's problem, I would first recommend disconnecting the ground wire from the battery. 

If I am following your post correctly, in addition to the engine shutoff, you have strange things happening with lights and wipers, right?  A burned fuse contact is of concern as it could indicate some crossed wires or wires grounding out.  Look under the dash, along the steering column and the backside of the fuse box for evidence of melted insulation, paying particular attention to any wiring going to and from the ignition switch, wiper switch, wiper motor, and headlamp switch and instrument lighting.  Also check to see if items in motion under and behind the dash, like pedals and pedal linkages, steering shaft, wiper motor and linkages, etc., are brushing against wiring anywhere.  If you find any damaged insulation, take note of the color(s) of the insulation and check your car's wiring diagram to see what it is supposed to power.  You'll want to trace the wire as far as possible to insure there is not additional damage down the line.  It is also wise to check the general condition of the wiring harness where it passes through the firewall and other points in the body.  If the rubber grommets have perished then the wire bundle can be fraying against the metal, grounding out hot circuits. 

[larryled]

Folks, thank you for all your inputs.  I just haven’t had time to Put some of your suggestions to test yet, but will soon.  What I eventually find I will pass on thru a Post.  Larry