Electrical Short Problem - Mercedes-Benz Forum

 
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post #1 of 6 (permalink) Old 11-06-2006, 02:48 PM Thread Starter
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Date registered: Aug 2005
Vehicle: 1976 W116, 450SE --- 1981 W126, 380 SEL--- 1972 W108, 280SEL---1963 W111, 200S
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Electrical Short Problem

FUSE #5 constantly blows.
used for: parking/tail/standing right, licence plate, instrument, hazard warning flasher, shift indicator illumination, side marker lamps

How can I troubleshoot?

Also, my headlight switch : Problem is when I take off the emergency brakes the lights turn off + hard to turn on... will replace the switch..

worried more on troubleshooting what wires are bad..
thanks!

other than that, car is great... gotta change the shifter bushings... they are crumbled...

thanks in advance! will post pics of the car now and the later....

It's not all that, But it's mine.
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post #2 of 6 (permalink) Old 11-07-2006, 03:26 AM Thread Starter
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Date registered: Aug 2005
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headlight switch problem fixed.
waiting on a electrical guru to give me insight on how to troubleshoot my car's constant fuse-blowing problem.
thanks!

It's not all that, But it's mine.
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post #3 of 6 (permalink) Old 11-08-2006, 08:47 PM Thread Starter
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ok. used the relays from my 380SEL and put new fuse. checked signal lights and fuse ok. started "pumping" the brakes and fuse out. Now gotta see if theres a wire peeled, etc... it's a learning process. hope someone will put 2cents and teach a easier way to troubleshoot.

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post #4 of 6 (permalink) Old 11-08-2006, 08:49 PM
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Wiring stuff like this is just grunt work. There is no other real solution, hence the lack of responses. Good luck -- I sure hope you sort it out.

"If spending money you don't have is the height of stupidity, borrowing money to give it away is the height of insanity." -- anon
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post #5 of 6 (permalink) Old 11-09-2006, 11:43 AM
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Arrow Basic troubleshooting for shorts

Here's two bits from an old retired Electrical Engineer:

1) DISCONNECT both battery terminals LEADS from the battery
2) Switch an Ohmmeter to its lowest scale (most sensitive)
3) Put the black meter probe on the Negative lead that was on the battery (-)
put the red meter probe on one side of the fuse #5 holder (fuse removed)
4) - record the reading: a) before pressing the brake pedal
b) while pressing the brake pedal
5) Repeat for the other side of the #5 fuse holder

YOU ARE LOOKING FOR A LOW READING TO GROUND TO DETERMINE IF THERE IS A SHORT TO GROUND SOMEWHERE THROUGH A WIRE OR COMPONENT.

i.e. I=E/R , I=12volts/your reading=less than the value of the #5 fuse

IF THE VALUE I IS TOO HIGH (and we know it is because the fuse blows) BECAUSE
R MEASURES LOW TO GROUND (-), TRY MOVING AND SHIFTING WIRES (AND LEADS TO NEARBY COMPONENTS) THAT LEAD TO THE FUSE BLOCK WHILE THE OHMMETER IS READING LOW RESISTANCE TO GROUND. YOU WILL NEED A BRICK OR A FRIEND TO HOLD THE BRAKE PEDAL DOWN, WHILE YOU INVESTIGATE.

This is how you start the troubleshooting proceedure.
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post #6 of 6 (permalink) Old 11-11-2006, 03:42 PM Thread Starter
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well, thanks for the responses. I pulled the tail light cover off and noticed a wire without protection. (both sides same). I also noticed one of the bulbs was "just there".. (the glass of the bulb not attached to the connector butt)/
I replaced the bulb, and threw some liquid tape onto the wires and no fuse blown yet... hope this worked.

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