jwSubMOA

My 87 S4 has a very high end stereo system installed by the PO. Long story short it is a Alpine head unit, custom sub, complete speaker replacement plus custom door panel speaker enclosures along with 2 amps and crossovers.It sounds great minus some ground issues I found. last week I was cleaning up some cooling fan wiring under the panel next to the passenger seat. I discovered one source of whining here, as the relay for one of the added fans was grounded to the noise suppression choke bracket. Yeahhh more better now! I then looked at the noise suppression coil that appeared to be no longer used in this install. I removed it and checked the pins on the plugs, 12v at one and 8.5V or so at the other. When I tried to turn on the stereo it had no power. Plug the choke back up, boom power .So I made a wire to connect the pins and remove the choke for ****s and giggles. Afterwards the stereo worked fine and greatly reduced whine from the relocated ground. Here is the weird part. My radio has never picked up stations, I assumed the booster needed attention. After removing the noise suppression choke, I pick everything up clear as a bell. WTH? I looked at the WD but it does not make sense to me. Any thoughts on this?

GJB928

Noise suppression choke was tied into amplified antenna wiring also?

Mrmerlin

for posterity,
this thread title will not send anyone here to find out what you have about your electrical system.
I would suggest to change it so others may find it in the future

linderpat

yes, amend the title. I clicked this just for kicks, but turns out I need to follow because I am having radio reception issues with my aftermarket system in my 85.

Michael Benno

I too would like someone to explain how the choke works.

I can tell you that the stock wiring does not power the antenna from that location (choke connector). The antenna should be getting power from the head unit. If the aftermarket head unit you have does not have an output for an antenna (which would be odd) then it's likely it could have been powered by the constant 12v line (small red wire) on the OEM loom. This wire receives voltage from the output site of the choke. It's the small red wire coming out of the connector to the choke. If the choke was not connected, then there is no constant voltage back to the factory radio plug.

The installer of your head unit would have needed to get constant 12v from another source (clock or cig lighter). Both of which will give you whining noise (BTDT).

Here is a good example of the factory connector (disregard the green/brown wires in the picture). Notice the white connector, that is the factory connector.
- The brown is ground and connects just above the CE panel.
- The thick red is your switched 12v (15amp) and comes from the ignition switch through a noise suppressor relay on the CE panel.
- The white is your antenna in you can see it takes two positions in the radio connector and then follow it out to a single white connector - that goes to the antenna amplifier.
- The thin red wire is your constant 12v (5amp) supply and that gets it's power from the choke connector at the right of the passenger seat


Here is a pic of the choke location on the passenger side. The brown and red wires taped off are for the OEM amplifier. The thick brown wire goes to the ground point above the CE panel. The thick red wire is 12v (15amp) from the connector to the choke.


FYI, the 12v (15amp) power supply to the choke and subsequent AMP and radio is supplied from CE panel from fuse #22 (Radio/Booster).

Here is a wiring diagram that I amended with my notes since I too was trouble shooting whining noise in my system. My choke was also disconnected and the installer used the clock as the 12v constant supply because the thin red wire in the harness was 'dead'. connecting the choke allowed me to power my radio as intended and thus the noise was eliminated.



The important thing to note with noise is that all power sources to the radio should be filtered. The radio has TWO sources of power: 1. Main power is switched from the ignition. This is filtered via the noise suppression relay on the CE panel. 2. Memory power is constant and is filtered via the choke on the passenger side. There could be other sources of noise in your system but these are the big ones. For more reference on noise review this: http://www.crutchfield.com/S-1qwh3Sh...ion_guide.html. I just spent a bunch of time doing something similar to the information is all still fresh.

Hope this is useful.