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Subject: Alternator Whine Fixed Author: Brian (moderator) : member since January, 2005 : 8586 posts Posted on: 2005-08-22 09:42:20

I have had an annoying alternator whine through the audio ever since I upgraded to a new gen radio. Back in February, when I was having trouble getting the new gen radio to work in the car, I noticed that my old gen radio plug is different from most other board members—it did not have negative wires (-) for the front left and right audio signals that run to the DSP amp. These are pins 8 and 11 on the 17-pin radio plug. The wires and pins were simply missing, as if they had never been there. As soon as I heard the whine, after I got the new gen radio installed and working, I knew that this was the cause, but I just now got around to fixing it.

Initially, I assumed that I would have to run completely new wires from the radio plug to the DSP amp. However, when I unwrapped the first 6” of the radio harness wiring, I found my negative audio wires. They were folded back and spliced into the chassis ground on the radio harness. This was done at the factory, because the length of the ground wires extended about 4” beyond the length needed to reach the radio plug. If it was done after the fact, then the wires would have been shorter then the length needed to reach the radio plug.

Original radio harness with the L & R negative wires spliced to the chassis ground
(You can see that pins 8 and 11 are missing)


My guess is that BMW was having alternator whine problems in the early cars, and this was their solution. (The cause was probably a ground loop, where the amp and the radio were not perfectly grounded.) This splice solution would only work if the radio’s audio negative connections were also grounded to the chassis. I am guessing that this was the case with the old gen radios, but not so with the new gen radios. This created a “floating ground” in the new gen radio, which is a leading cause of alternator whine.

My first challenge was to find the reprlacement pins for the radio plug. The RealOEM database was very handy (replacement pins on RealOEM), but it was not clear from the diagram and descriptions which pins I needed—so I ordered a set of everything that looked remotely similar. All of the pins I ordered would have worked, but one was more perfect than the others. The differences between them are the gauge of the wire pigtails connected to the pins and that the some of the pins have a plastic strain relief or insulation shield where the wire crimps to the pin. I used the pins with PN 61.13-000 7 449 (reference 4 in the RealOEM link), because the wire gauge looked the same as the audio wiring and it did not have the strain relief thing. The pins with the thicker gauge wire looked the same the wiring used for the power and ground connections (The pins themelves were identical.) Now I just have a lots of left over radio plug wiring pins to find a creative use for.

Replacement radio plug pins with wire pigtails that I spliced back into my radio harness


The repair probably took me less than 15 minutes to complete (not including disassembly and reassembly). The biggest hassle was simply removing all of the junk in the trunk to get to the radio. This would probably only be applicable to a small number of cars. Everyone with cars 1998 or newer with at least MKII navigation seemed to have the L&R negative signal pins. My car had a MKI navigation and was built in 7/1997, so this problem may only be present in the navigation equipped cars built prior to 9/1997, which are very few. And then, you will probably only get the alternator whine problem if you upgrade to a new gen radio.

Repaired radio plug harness with all of the signal and ground connections as they should be

• Alternator Whine Fixed (pic) (url) - Brian 2005-08-22 09:42:20 (1654 views)
  • Once again sherlock, good job! (nt) - silber98 2005-08-22 14:21:43 (224 views)
    • Thanks for posting the picture of your plug back in Feb. - Brian 2005-08-22 14:48:23 (219 views)
  • Interesting that your harness had been modified like that. - jcarey 2005-08-22 10:59:01 (230 views)