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From digest.v6.n883 Tue Jul 15 19:53:17 1997
From: <> (John Kitzmiller)
Date: Tue, 15 Jul 97 6:41:58 EDT
Subject: electrical gremlins <E28>

Thanks to all that responded to my question re the "check" light and brake light warning indicator. Apparently what I have is not a glitch, but a feature. Next time I'll RTFM before asking.

With regard to the OBC and radio going out, they went out again this morning as well as the tach and 4-way flasher. I checked the fuses, wiggled the appropriate one, and, mirabile dictu, the problem was solved. At Don Eilenberger's suggestion I'll replace the lead/tin-based fuses with copper-based, clean the fuse holders, and tighten them just a little bit.

For the problem of the radio shutting off when the brakes are first applied, I'll try one of the following, furnished by Scott Buchanan: From: Jeff Wilcox <>
Date: Tue, 17 Sep 1996 01:39:19 +0000
Subject: re: E28 stereo wiring

Jonathan states his problem is power being cut off to his stereo when he steps on the brakes. Been there. Had that same problem with my aftermarket stereo. What brand did you buy? Not that it matters, just curious. I have a pioneer.

Anyway, the fix is simple enuf. What I did (if I remember correctly) was stick my voltmeter into the ignition controled wire, then stepped on the brakes. I wanted to see the voltage drop occur. Sure enuf it did. I bet you also hear a periodic pop from the speakers when you apply the brakes, that is, if the stereo doesn't turn off first.

After you check the ignition line, find a hot lead (ie one that is always hot). Check it also for the voltage drop when brakes are applied. What you'll probably find is that it too drops, but not nearly as much. By the way, I did the voltage drop tests with the car running.

Now you have two solutions....

  1. Connect the radio to the continuously hot lead. This will let you turn on the radio without the ignition on. You may or may not be able to hear anything depending on whether and how you have an external amp hooked up. I chose not to go this route.

Rather... I did this...

2. Buy a simple relay at Radio Shack. Look at the wiring diagram on the box and connect the hot lead to the incoming line, the stereo power line to the outgoing line. Now you can use the ignition lead as the trigger to trip the relay and power the stereo like before, only the brake related problems should vanish.

Hope this helps some. I suffered thru this same problem for a couple of years before some smart guy at Circuit City suggested the relay trick.

As always, YMMV
Good luck
Jeff Wilcox
88 535i 93K

To all who had the radio problem. Here is a cheap easy fix that should work. Go to any electronic store or car audio shop and get a cap. Get a relatively small one but one that will hold enough juice for about 5 seconds as your voltage drops when you hit the brakes. Good luck Rob

Many thanks to Robert Andrews, Walt Barie and Ken ( and all other digest contributors for their responses to my aftermarket stereo woes. t was reassuring to know that the brakelight voltage drop triggering a stereo shutdown was not a gremlin unique to my '87 535is.

I called Blaupunkt (Robert Bosch) technical assistance who didn't sound familiar
with my problem but they recommended either of 2 solutions:

  1. Install a 500 - 1000 mF capacitor accross the switched (+) power source to

    the radio and black ground wire. This will act as a mini-backup power supply when a voltage drop hits, thereby keeping voltage constant.

  2. Alternatively to #1, install a small 12v relay that is switched on by the

    oem purple/grey switched (+) radio lead. The 12v relay will withstand the

    voltage drops caused by the brake lights and keep the power source to the

    radio constant.

From: (Curtis A. Ingraham)
Date: Sat, 9 Nov 1996 22:45:46 -0800
Subject: <E12> Radio Cutout w/Brake

Guy Jeffress <> wrote:

> I own a 1979 528i and I am having trouble with my radio.
> Whenever I hit the brake the radio goes off, when I release
> the pedal the radio power returns.

This problem got a good thrashing recently on the Digest, and it occurs in E28s as well as E12s, as I recall. The switched power lead for the radio is on the same fuse as the brake lights. The voltage on this circuit dips when the load of the brake lights is applied, and some radio models are so sensitive to this dip that they switch off. Some radios recover in a second or two as the brake light bulbs heat up (increasing their resistance and decreasing their load on the circuit).

If this is a recent problem, you might fix it (maybe temporarily) by installing a new fuse and tightening the fuse clips.

The permanent solution is to install a relay for the radio power. Buy a generic Bosch relay with four terminals and normally open contacts. The kind sold for use with fog lights is fine. Find and cut the switched power lead to the radio; this one is off when the key is off and on when the key is in the first position. Connect the relay as follows:

  1. Connect the wire end from the radio to one relay contact.
  2. Connect the wire end from the fuse to one end of the relay coil.
  3. Connect the other end of the relay coil to ground.
  4. Finally, connect the other relay contact to the power wire for

    the cigarette lighter.

With this arrangement, the radio/brake_light fuse will turn on the relay, and the relay will switch the more solid cig lighter power to the radio.

Curt Ingraham

>My 1986 528e has developed a problem that seems to have to do with the
>stereo system and the brakes. I have the stock, 6-speaker
>cassette/stereo that came wih the car 10 years ago. Whenever I am
>listening to the radio or a cassette, and I hit the brakes, the console
>(i.e. OBC and radio display) lights dim, and there is a single, audible
>CLICK over the radio, which sometimes is barely noticeable, and
>sometimes actually interrupts the playing of the cassette I'm listening
>to. This will also occur to a lesser extent when I initiate the
>turn-signal. And recently, I'm getting some very loud and irritating
>static any time I try to adjust the volume on the stereo.
TIA - Eric

I had EXACTLY the same symptoms on my 1986 525i with a Pioneer stereo, I decided to re-wire the radio-to no avail. The radio had a permanent 12v for the memory and as a main power source and an ignition controlled one just to tell the unit to power up.

I beefed up the continuous power connection with a wire straight from the fusebox, but this mad eno difference, even straight from the battery! I checked the -ve earth which didn't do anything either.

The problem was the low power ignition-controlled connection which plugs into a white nylon cluster of sockets about 4x4 inches to the right of where the steering column exits through the bulkhead (ON A MY RHD CAR)

I found that all of the sockets on this connector which give a 12v ignition switched output give the brake light glitch.

I had to run a wire from an ignition controlled fuse under the fuse box. (There are spare blade connectors under some of the fuses that you can plug a lucar connector onto)

Hope it helps, RCC

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