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E28 (1982 - 1988)

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  #1  
Old 08-17-2009, 09:43 PM
Groundsel Groundsel is offline
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Location: California
 
Join Date: Aug 2009
Posts: 2
Mein Auto: 528E
Need Help to Diagnose Electrical Problem-Brake Light/Speedo/Radio

Hi -

Today I was driving my 88 528E, 275K miles. I applied the brakes and the following all happened simultaneously:

Brake light warning light came on.
Speedometer went to 0 and stayed there. Both odometers stopped rolling. Stereo powered off. All other electronics were OK. RPM and other dash gauges were OK.

About 15 miles later, I hit a bump and the radio, speedo and odometers sprung to life again. The next time I applied the brakes, they all died again, and remain dead. (Further bumps did not fix it again.)

Any ideas? Brake light switch maybe? What do the speedo, odometer brake lights and radio have in common electrically? I could not find any similar cases in these forums or google.

Thanks!
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  #2  
Old 08-18-2009, 12:17 AM
Groundsel Groundsel is offline
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Location: California
 
Join Date: Aug 2009
Posts: 2
Mein Auto: 528E
Need Help to Diagnose Electrical Problem-Brake Light/Speedo/Radio

More info. Brake lights are really out. Radio is not stock.
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  #3  
Old 08-18-2009, 02:00 AM
86BlueDoor 86BlueDoor is offline
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Location: New Mexico
 
Join Date: Jan 2009
Posts: 40
Mein Auto: 1986 528e automatic
I've dealt with similar problems. My problem was the after-market radio and external amp was wired 'improperly??' so that when the brake was pressed there was a loud 'click' sound from the speakers. Eventually this would cause a 'short' to occur and effect the cluster gauges.
First, check your fuses...especially the radio.
Secondly, the brake warning light (not on cluster) tells you that one of your brake light bulbs is out.
(Did you notice this warning light anytime before this time?)

This is how I sorta corrected the problem:
Short version- I ran a single hot line (with in-line fuse 15 amp?? maybe 30amp??) directly to the brake light switch (on pedal). This removed the 'extra' charge, each time I braked, to the electrical system.
Long version- I found that the after-market radio/10 disc changer was 'bad' and I removed it and found an factory radio/cassette radio to replace it with. Because I had no factory harness to just plug into, I had to figure out 'more or less' which wire went where and sorta re-wired the radio sound system (including the external amp). No more 'shorts' in electrical system.

BTW- The factory radio/cassette came from the junkyard ($10) and the cassette does not work as well as some of the buttons. However, I needed it to 'figure out' the original wiring and system in my 86' 528e auto trans. I do plan to replace the radio with an new radio/cd system eventually....need more $$$. Good luck!
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  #4  
Old 08-22-2009, 01:04 AM
fast.work fast.work is offline
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Location: california
 
Join Date: Aug 2009
Posts: 39
Mein Auto: BMW M5
I can just say that its quite clear that there is defineltely a problem with wiring.Could be any of the following:

Loose wirig
Improper wiring
Fuses
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