Radio Head Pin-Outs, Wire Color, Harness Adapter and Security Unlock Code information for the radio on a stock 993

Below are the complete 993 pin assignments and functions for the Block A harness a superset of what is specified in the diagram above:

For Block  A:
Pin 1: speed-dependent volume control (white w/ red stripe), faded from age can look brown stripe
Pin 2: (no connection) telephone mute
Pin 3: Not specified
Pin 4: +12V constant (red)
Pin 5: antenna power (white)is a short run and plugs into small spade connector of black wire coiled around your antenna cable to power the antenna amplifier box
Pin 6: illumination (grey w/ blue stripe)
Pin 7: +12V switched ignition (red w/ black stripe)
Pin 8: ground (brown)

For Block B:

Pin 1: Speaker Right Rear  Positive  Red                 (Left Hand Drive)

Pin 2: Speaker Right Rear  Negative Brown & Red   (Left Hand Drive)

Pin 3: Speaker Right Front Positive   Black              (Left Hand Drive)

Pin 4: Speaker Right Front Negative Brown & Black (Left Hand Drive)

Pin 5: Speaker Left   Front Positive   Wite               (Left Hand Drive)

Pin 6: Speaker Left   Front Negative Brown & White (Left Hand Drive)

Pin 7: Speaker Left   Rear  Positive   Yellow              (Left Hand Drive)

Pin 8: Speaker Left   Rear  Negative Brown & Yellow (Left Hand Drive)

For Cars with a Block C wiring harness termination present:

CR-1 Pigtail connectors
Blocks A, B & C

2/6/2022, Per my discussion with Rennlist member TBO12, Steve informs me that on his 993 equipped with a CR-1 radio head and the premium sound option the C-Block Plug is present behind the dash as part of the wiring harness. If found to be present on your car the pinouts are as follows:

Pin 5: Audio output ground;

Pin 6: Switched (+) power to the amp so it acts as a slave to the radio head;

Pin 7: Front right line level out to external amp input;

Pin 8: Rear right line-level output to the external amp input;

Pin 9: Front left line-level output to the external amp input;

Pin 10: Rear left line-level output to the external amp input.

On the CR-1 radio head, the round DIN connector attaches the external Compact Disc changer option.

If a previous owner cut off the original wiring harness plugs above to attach an aftermarket radio, here is a source for replacement plugs: 
https://www.suncoastparts.com/product/91164529900.html

For Cars with the Nokia power amp:

Nokia amp. circuit board with radio head
connection socket to left circled in red.

On Premium Sound System-equipped cars the round harness connector under the seat plugged into the power amp feeds a switched (+12V) signal and line-level preamp signals to the amp from the Block-C connector behind the radio head. Be aware the switched (+12V) signal wire is only to trigger the power amp to turn on. High amp power to the power amplifier is then fed to it through a dedicated constant-on hot wire under the seat.
Here is the Nokia amp connector's pin-outs:

  

Switch on Radio 
Mounting Frame

Radio Alarm Anti-Theft Switch 

There is a spade terminal with a green wire that attaches to a switch on the radio mounting frame that leads to the alarm module.

The switch acts as an open switch when the radio head is in position. When the radio head is removed it grounds the green wire to a body ground through the radio mounting frame triggering the alarm. If an aftermarket radio is added this spade terminal should be insulated and tied off where it can't accidentally touch a body ground. If grounded it will interfere with the proper operation of the alarm.

It has also proven to cause problems when the OE radio is disturbed and can be tied off to eliminate alarm issues stemming from the radio mount going forward.

Below is a listing of the Pin-Outs on the OE Nokia Amp. This form includes a correction of an error in the description of pins 14 & 15 on the amp.

OE Radio head security code. 

If you have removed the stock radio and plan to reuse it you may need to enter a security code to unlock the radio. It can be gotten from the dealer if the radio is original to the car, having not been upgraded at the Dealer or swapped out some time in the past.

The below website is a more economical source for the radio security code that like Becker as a source can provide the correct code for a specific radio whether or not it was original to the car:

http://www.radio-code.co.uk/ 

All that is needed to get the Radio security code for all Porsche & Becker branded radios supplied in the 993 is the last 4 digits of the serial number on the radio chassis.

Wiring Harness Adapters:

If you are looking for a comprehensive source for adapters for the wiring harness to avoid cutting and pasting wires here is a great source for these items:

https://www.bergvillfx.com/categories/wiring-harnesses

For example, to install a modern Blaupunkt Bremen SQR 46 DAB one will need Bergvillfx's "Audio harnesses to install in a Premium Sound System-equipped car.

11/28/2022 Warning attributed to Rennlist member Jwong1977:

"The [Nokia amplifier wiring adapter] harness I received from Discount Car Stereo had one major mistake, it had the colors of the ground and power reversed on the harness! So instead of power being Red and Ground being black, it was the other way around. I caught this as I was studying the pin-outs on Andy's page. It shows there that 5-6 were ground and 10-11 were power. It's no big deal as long as you route the correct cable to the amplifier, just be careful and check twice or three times if needed."

Below is the wiring diagram for the remainder of the OE audio system, both Standard & Premium optioned components, pinouts, and wiring:

Here is a URL to a high-resolution audio wiring diagram. suitable for printing off.

 

Installing the Blaupunkt Bremen SQR 46 DAB is a common upgrade for our cars. I found the pinouts for this radio below in the online manual. 

It does not support a Block "C" line-level output plug on the stock 993 wiring harness but in its place are RCA-style sockets for the 4 channels and a powered subwoofer.

Preserving the Nokia Amp:

If your car is equipped with the Premium Sound option and you would like to preserve the Nokia Amp under the seat. One can consider making an adapter cord that runs from behind the Bremen head to the Nokia amp under the seat. 

The cord will be a bundle of cords including 

• 4 shielded wires with RCA plugs on one end soldered to the shared 8-pin DIN connector on the other end for the 4 audio channels, Left & Right for Front & Back and an additional 
• switched hot (+) wire from Pin 4 Block "A" to the round DIN plug on the other to plug into the Nokia amp.  

The easiest way to make the cord is to buy four two-meter RCA to RCA cords and cut one end off of each cord and solder it to an 8-pin DIN connector using the pin-out diagram above. The needed switched hot wire from the head to turn the Nokia amp on and off can just be a length of primary wire bundled along with the shielded RCA cords soldered to the DIN end. Tore may offer an adapter for this. If not the parts are easily purchased from Allied Electronics & Automation. or even eBay to fabricate your own DIY.

A behind-the-radio head wiring harness adapter:

Another approach is to buy the 10 Pin ISO radio socket pigtail (not the harness plug) that will mate with the block "C" wiring harness plug behind the radio head and solder 4 short cords

Radio Socket Pigtail

with RCA plugs on the end and include the switched hot wire connection to turn the Nokia amp on and off. In this way, the existing harness running down to the amp under the seat can be used. 

The pigtail and RCA cords with plug ends can be found on eBay.

RCA Plugs

Installation where the Nokia Amp is abandoned and the power amps in the head are used:

In this case, unplug the Nokia amp under the passenger (LH drive) seat and run new speaker wires from the Bremen head block "B" to the Nokia's wiring harness plug using Tore's Nokia amp plug pigtail.

Since the Nokia is a bi-amplified unit using two amplifiers to power each door's speakers an additional two-way hight-low passive crossover for each door will be needed to join the three speakers to the now common amplifier in the Bremen. 

The amplifier in the Bremen provides 24 watts RMS/50 peak per channel and so has a useful amount of power and may actually sound better than the stock Nokia amp.

The tweeter in the door has its own crossover in its housing so only a two-way crossover is needed not a three-way if you plan to use the existing wires to the doors.  That crossover can be positioned under the seat at the OE power amp harness connector with its inputs attached to the front L/R speaker wires from the head and the two crossovers' outputs one feeding the woofer in the door and the other feeding the combination of the midrange & tweeter attached through the appropriate pins on the Nokia amp's wiring harness plug. 

The crossovers can be purchased inexpensively online from Best Buy, Crutchfield, eBay

A typical two-way crossover

or really any audio component retailer and will not only manage the frequencies to each driver but will also manage the total load on the power amp output avoiding damage to the radio head if a crossover is not used.

A Continental Radio

Continental Branded radios have also become popular as they also look somewhat period correct. They are a good choice if you do not plan to use an external power amp or reuse the original Nokia amp as the Continental heads do not have bloc "C" or RCA-type line-level outputs for use with a power amp.

Continental Radio
Blocks A & B

Continental Radio Block Connector Pinouts

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