Pagoda SL Group

W113 Pagoda SL Group => Electrical and Instruments => Topic started by: tdun824259 on September 22, 2007, 21:15:14

Title: RPM Drop with Bulb Upgrade.
Post by: tdun824259 on September 22, 2007, 21:15:14

I recently went through the headlights, tail lights, side markers, and turn signals and up graded all bulbs.  It may be just coincidental but I now notice a dramatic drop in rpm when turning on the headlights.  The car will immediately idle rough and eventually die with the headlights on.  If I turn off the lights quickly enough the rpm will return to normal.  At speed the car runs just fine.  If I pull up to a stop light I need to be prepared to turn off the headlights or I'm in trouble.  Any ideas?

Thanks
Tim Dunagan
1971 280 SL

Title: Re: RPM Drop with Bulb Upgrade.
Post by: jeffc280sl on September 24, 2007, 07:51:21

The simple answer is that you are drawing too much current from the electrical system.  I doubt going to higher wattage bulbs would cause this kind of stress on the alternator.  It's possible you may have moved a wire and created a short somewhere.  I would go back throught the wiring for each bulb starting with the head lights to check.

Jeff C.
1970 280SL 4-speed

Title: Re: RPM Drop with Bulb Upgrade.
Post by: tdun824259 on September 24, 2007, 10:45:16

Thanks Jeff,

I'll retrace my steps!  I do have the side markers set up to flash with the turn signal indicator.  I'll do some checking.

Tim Dunagan
1971 280 SL

Title: Re: RPM Drop with Bulb Upgrade.
Post by: jeffc280sl on September 24, 2007, 13:16:10

My side lights are set up to flash also.  Is that something you did when you replaced the bulbs?

Jeff C.
1970 280SL 4-speed

Title: Re: RPM Drop with Bulb Upgrade.
Post by: tdun824259 on September 25, 2007, 07:59:07

Jeff,

No, the side markers were flashing before the bulb update.  I have Euro headlights if that matters.

Tim Dunagan
1971 280 SL

Title: Re: RPM Drop with Bulb Upgrade.
Post by: jeffc280sl on September 25, 2007, 09:35:24

Tim,

Thanks for the info.  Just thought you might be able to narrow down the issue by removing fuses one at a time. Here is a list of the fuses and which lamp it serves.

12  L low beam
11  R low beam

10  L hi beam + flash to pass
9   R hi beam + hi beam indicator

You could remove these fuses one at a time and see if things improve.  If it does then that fuse will indicate the problem circuit.

Same goes for the following.

8   L prkg lights
7   R prkg lights + dimmer for dash lights  

All of these circuits should have 8 amp fuses.  Check to make sure you have the correct size.  Let me know how you make out.

Jeff C.
1970 280SL 4-speed

Title: Re: RPM Drop with Bulb Upgrade.
Post by: tdun824259 on September 25, 2007, 11:05:10

Thanks again Jeff,

It will be my Thursday project.  I'll keep you posted.

Tim Dunagan
1971 280 SL