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Old 02-09-2008, 08:27 PM
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Join Date: Feb 2008
Location: san antonio
Posts: 3
W140 Brake pedal blows fuse

First time poster---long time reader. I have a 1998 s320 with 119k. My electrical woes began when I left for work to find my battery was dead. I replaced the battery and 3 days later the same problem. I exchanged the battery and began driving the car again. A friend was following me and said my brake lights were out. Later that afternoon, my battery was dead again. I need to clarify that when I say dead, I mean 0 volts and no charger could revive it. Today I went to Advanced Auto and they were kind enough to exchange my battery AGAIN. I began pouring through the forums and found all of the testing methods for an electrical system short. I removed the negative cable and checked with my multimeter for a draw, measuring from the negative post to the negative cable lead. I also tried across the positive side. I could only get a reading of zero with two different meters. I then checked to see if there was voltage, testing at the same location. There was 12 volts measuring from the negative lead to the negative post. So thinking that I had found something I ran jumper cables to the front of the car from the post and the cable lead and began removing fuses. I checked every one indiviually and then removed ALL of them. I discovered that fuse #21 (wiper heater, mirrors and climate control) was burned. So I replaced the fuse started the car, and..... the dummy light for burned out bulbs( which was on before) was now off and I thought that I found the problem, until I stepped on the brake and the fuse blew again and the dummy light came back on. Any help pointing me in the right direction could save my sanity. To recap, any clarification on the testing method would help, like

what setting should my meter be on (had it on dc amps- tried 2 and 20 Ma

I should be testing from the neg post to negative cable??

Should I be reading voltage across same spots (tried my wifes 06 jetta and read 11 volts across neg cable and neg post)

What could cause the depression of the brake pedal to cause a fuse to be blown?

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Old 02-11-2008, 08:06 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
The most common problem that causes thatr fuse to blow is the 3rd brake lamp. Many times the electrical housing will melt.

The best way to check for a draw is measuring the current flow with an amp meter between the negative cable & battery post.
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