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Author Topic: Headlights dim while driving  (Read 10460 times)

hauser

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Headlights dim while driving
« on: September 05, 2007, 23:55:27 »
Took the car out tonight for a drive.  While driving down a poorly lit street I noticed somethig was going on with my lighting.  The lighting intensity would change from bright to dim and back to bright.  The only electrical work that's been performed on the car was the installation of a rebuilt Bosch 55 amp alternator.  The engine is running strong and the rpms didn't seem to effect the problem.  I have no clue what is causing this.

1969 280sl 5 spd
Gainesville, Fl.
« Last Edit: September 06, 2007, 20:47:46 by hauser »
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Jonny B

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Re: Headlights dim while driving
« Reply #1 on: September 06, 2007, 05:49:10 »
Did you notice if anything was going on with the alternator light, was it dimly glowing? Any correlation with road bumps? i.e. a loose ground? Was it both lights? How about the bulbs themselves, could they be ready to burn out?

Jonny B
1967 250SL Auto
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Jonny B
1967 250 SL Auto, DB 568
1970 280 SL Auto, DB 904
1966 Morris Mini Minor

hauser

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Re: Headlights dim while driving
« Reply #2 on: September 06, 2007, 07:47:49 »
No, the indicator light did not come on.  No road bumps or loose surface.  I'll change out the regular headlight bulbs with halogens I purchased from Daniel Stern.



1969 280sl 5 spd
Gainesville, Fl.
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jeffc280sl

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Re: Headlights dim while driving
« Reply #3 on: September 06, 2007, 10:28:56 »
I suspect the headlight fuse is dirty.  Try gently compressing the fuse holder with your fingers and spin the fuse in its holder. That should take care of it.

Jeff C.
1970 280SL 4-speed
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waltklatt

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Re: Headlights dim while driving
« Reply #4 on: September 06, 2007, 14:50:37 »
Hauser,
Think the headlights are robbing the ground through another source.  Check the ground wires for the headlights.
Walter
1967 220SL-diesel, new heater and A/C almost in.
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glennard

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Re: Headlights dim while driving
« Reply #5 on: September 06, 2007, 20:12:35 »
Suspect the 'Boch'!
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hauser

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Re: Headlights dim while driving
« Reply #6 on: September 06, 2007, 20:50:49 »
The Boch[:0] is now a Bosch ;) !  But it still doesn't solve the problem.[:(!]

1969 280sl 5 spd
Gainesville, Fl.
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Benz Dr.

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Re: Headlights dim while driving
« Reply #7 on: September 06, 2007, 23:11:37 »
Not likely any of those things. Grounding is the first thing to check but it could be a bad headlight switch. I know on 190SL's all the power goes through the switch and then to the ignition. I had a car that had a strange miss that I couldn't locate but only at night. The switch came loose when I turned the knob so I reached under the dash to hold it so I could turn off the lights and burned my hand on the housing. It's not supposed to get hot at all. I put a new switch in and it ran like a new car after that.
Try and see if the switch gets hot after driving at night for a while. Of course, you had the charging system checked out, right?

Dan Caron's
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benzbarn@ebtech.net
 slbarn.mbz.org
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1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
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1970  3.5 Coupe
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1985   300CD  Turbo Coupe
1981  300SD
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1967 250SL
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hauser

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Re: Headlights dim while driving
« Reply #8 on: September 07, 2007, 21:06:49 »
The switch is nice and tight.  All of its fuctions (Euro) are working properly.

It's very similar when a car is about to stall and the lighting goes dim but it to normal again.  When I noticed this problem I even tried reving up the engine but it didn't help.

1969 280sl 5 spd
Gainesville, Fl.
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Markus

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Re: Headlights dim while driving
« Reply #9 on: September 07, 2007, 22:01:32 »
It would be interesting to note what happpens when you connect a volt meter to the system to help diagnose problem.  Is the voltage regulator an original?  They are only about 35.00 bucks for a new one online.
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hauser

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Re: Headlights dim while driving
« Reply #10 on: September 07, 2007, 22:38:43 »
The paper work goes back to 1978 and it's about three inces thick.  Off hand I don't remember seeing anything about the voltage regulator.  BTW the VR was my first suspect.

1969 280sl 5 spd
Gainesville, Fl.
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Benz Dr.

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Re: Headlights dim while driving
« Reply #11 on: September 08, 2007, 12:12:17 »
It dosen't matter if the switch is tight or loose or if it works properly - it can still be no good. Put your hand on it after it's been on for a while and see if it gets hot. It should be cool to the touch.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061
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1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

1970  3.5 Coupe
1961  190SL
1985   300CD  Turbo Coupe
1981  300SD
2013  GMC  Sierra
1965  230SL
1967 250SL
1970 280SL
1988 560SEC

al_lieffring

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Re: Headlights dim while driving
« Reply #12 on: September 08, 2007, 14:02:30 »
I'll back up Dan on this one.

I have seen lots of freaky electrical problems, many not related to the head lights caused by a defective light switch.
On Benz cars from the 60's and early 70's the main power suply for the entire car is bussed through the head light switch, the terminal where the main power lead is screwed to the switch will corrode and cause the switch to overheat. Possibly new ring terminals will need to be soldered to the affected wires too.

Al Lieffring
66 230Sl
Jones'n for a new gas tank
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hauser

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Re: Headlights dim while driving
« Reply #13 on: September 08, 2007, 23:28:39 »
Is the light swich the same for Euro and US models?

1969 280sl 5 spd
Gainesville, Fl.
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al_lieffring

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Re: Headlights dim while driving
« Reply #14 on: September 09, 2007, 06:23:22 »
quote:
Originally posted by hauser

Is the light swich the same for Euro and US models?

1969 280sl 5 spd
Gainesville, Fl.


Yes.

The switch is the same, the terminals for US and Euro are both there, the wires are just connected different. on my USA model, I have the fog lamp wires connected to work like the european models.

Al Lieffring
66 230Sl
Jones'n for a new gas tank
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