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Section I: Basic Info and Preparation

Section II: Disassembly

Section III: Wiring

Section IV: Reassemble

Project Summary

This document is meant to serve as a guide for those who wish to add heated seats to a Boxster that did not have it as a factory option. Section I is informational, regarding different approaches, preparation, and the resources required. Sections II-IV are a reference for the do-it-yourselfer (DIY), and provides step-by-step directions.

My main motivation for adding heated seats was to increase the number of "top-down driving" days. Even in Northern California, where the climate is mostly warm and sunny, there are days when having the top down is a bit too cool to be comfortable. PCA Boxster Technical Specialist Peter Smith encourages the sales staff to include heated seats in every cabriolet, as it is only a $500.00 option and hard to retro after. As you can see from a survey I hosted, it is considered a "must have" feature by most. I didn't think too much of heated seats until I became used to using the ones in my girlfriend's BMW. Now, much like my TiVo, I don't know how I ever lived without it.

Labor Summary

You will likely want to hire an upholstery shop to do the seat foam replacement work. This will leave the creation and running of the wiring harnesses throughout the car. This may include taking out the seats, console, and some of the dash, as well as accessing the fuse and relay panels. If you're willing to do the labor yourself, this is the most economical (and educational) route.

Cost Summary

Part and labor costs are an estimate based on my own experience. They may vary in your area. This estimate assumes that you already have the necessary tools, as well as basic mechanical and electrical skills. It does not include components like solder, wiring, etc.

ItemCost
Parts$815.86
Upholstery Labor$340.00
Two Seats Parts and Labor Total$1,155.86

Foreword

These instructions assume that you'd like to upgrade to a two-stage heating system for driver and passenger seats that is as close to the original P14 factory option specifications as possible. There are aftermarket mechanisms such as those offered by Check Corporation, or kits by PFYC that are made for other cars and may be adapted to the Boxster, but they will not provide stock look and feel. In addition, there are some instances that may allow you to use common electrical connectors, tap onto existing wiring, or select different wiring runs. I chose not to do this in order to provide stock look and feel, as well as minimize risk to other electrical components.

It is highly recommended that you gain access to the electric circuit (wiring) diagrams that apply to your vehicle. These are part of the multi-volume Porsche Boxster Technical Repair Manual that is used by Porsche Service Departments. Hard copies are available for purchase from most Porsche parts vendors for about $500, but are often backordered. I have also seen Adobe Acrobat (PDF) versions on eBay from time to time. Online versions of the diagrams are available from vendors like All Data Do It Yourself. It should also be noted that the National Automotive Service Task Force (NASTF), a not-for-profit organization, has driven auto manufacturers to make service and repair information for their models available to independant mechanics. For Porsche, this takes the form of Porsche Technical Service Information that provides technical documentation for Porsche vehicles.

Wiring Harness

Porsche does not make one harness for all cars. Each car has a different harness depending on the options the car was originally ordered with. Since you're reading this, your car probably didn't come with the heated seat option and it will be necessary to create and install an overlay harness to power heated seats in the car.

Building your own harness is the most economical path. Porsche Parts only sells a complete passenger compartment harness that comprises all electrical runs, and not just for heated seats. It runs in excess of $4,000. My local Porsche service department quotes $1500.00 to "create" and install an overlay wiring harness. This is just to run the wiring, and does not include the heated seats themselves or the parts/labor to upgrade the seat heating coils, switches, etc.. You may consider looking for a salvage car to obtain a used harness. Unfortunately, they are hard to come by and run the risk of being damaged. A final alternative is take your car to an independant shop such as Paris Audio who provide a variety of audio and electrical customization services.

Note Note: You can purchase the seat wiring harness (listed in the parts section), which connects the coils in the seating pads to the under seat heater relay. This is not the same as the main harness which provides wiring to the switches in the console, power from the fuse box, or connection to the bridge plug.

When building your own harness, here are the wiring runs that will need to be overlayed.

ColorGauge
(mm2/AWG)		RunLength
YE/WT.35/20Console to Passenger Seat13'
YE/BK.35/20Console to Passenger Seat13'
YE/RD.35/20Console to Passenger Seat13'
YE/WT.35/20Console to Driver Seat13'
YE/BK.35/20Console to Driver Seat13'
YE/RD.35/20Console to Driver Seat13'
RE/VI1.0/16Passenger seat to fuse panel11'
RE/VI1.0/16Drivers seat to fuse panel6'
GR/BL/RE.35/20Passenger switch to Drivers switch1'
BR.35/20Passenger switch to Drivers switch1'
BR.35/20Switch to dash ground (GP4)4'
GR/BL/RE.35/20Console to BS15 (relay)10'

Note Note: Porsche lists their wire gauges in mm2 (metric). U.S. manufacturers go by American Wire Gauge (AWG). Provided above is the wiring diagram listing in mm2, with the nearest AWG equivalent (rounded up to insure adequate capacity).

Wire Ratings

Since I created my own harness, I was very concerned with finding wire that was safe to use in a passenger vehicle. I could not find any official Porsche requirements or recommendations related to use of wires other than the gauge that is shown in the wiring diagrams. Conversations with custom wiring shops, wire vendors, and Porsche repair shops essentially led to the following conclusions.

While wiring from the hardware store might work, it is designed for AC as opposed to DC use. In addition, it may not provide the temperature, flexibility (resistance to kinking), and durabilty (resistance to abrasion and chemicals) that is needed for automotive applications. You may also find "automotive primary wire" available at your local auto parts retailer (e.g. Pep Boys). Conduct-Tite from Motormite/Dorman seems to be the dominant brand, but they don't list any ratings or certifications on their packaging or web site.

Things to keep in mind when purchasing wire are:

  • Temperature: Particularly for auto applications, the temperature rating of wire insulation is important.
  • Multiple-strand Wire: Single strand wire is least desirable where flexing is likely to occur, so it is rarely if ever used for automotive wiring. Multiple strand wire is less likely to fracture from repeated flexing, and the greater the number of strands, the more flexible the wire.
  • Gauge: The diameter of a wire affects the wire's ability to conduct electricity effectively.
  • Insulation: It's important that the insultation protect the wire itself from chemicals (e.g. gas, oil, etc.) and abrasion.

The most prevalent ratings that I could find for passenger vehicle wiring was from the Society of Automotive Engineers (SAE). Despite my expectations to find SAE and/or Department of Transportation (DOT) equivalent specifications required or recommended by Porsche, I did not.

Given the application, I chose to use TYPE TXL Extra Thin Wall (XLP) AUTOMOTIVE PRIMARY WIRE from Allied Wire and Cable. It is a low tension primary cable that is meant for the following applications.

  • For use in automotive applications where small diameter and minimal weight is desirable. Meets requirements of SAE J-1560 (now contained in J-1128).
  • Recommended temperature range -51 C to +125 C.
  • Available in solid colors and stripes with optional custom printing and/or numbering available.
  • Also meets Ford (Mil-123A) and Chrysler (MS-8288)

Tools

It's recommended that you have the following tools in order to complete this project.

  • Crimp tool
  • Fold-over crimp tool
  • Wire stripper
  • Multimeter
  • Flux
  • 60/40 tin/lead solder
  • Soldering iron (40w)
  • Torx socket
  • Torx wrench
  • Flashlight
  • Wire puller
  • Regular screwdriver
  • Phillips screwdriver
  • Wire puller/retractable claw tool
  • Heat gun
  • 1/16 and 1/8 inch shrink tube

Parts

Note Note: When ordering parts, keep in mind that color and style codes may vary by year and seat type. For example, A02 is gloss black finish on the tip switch. The following were used on a 1997 Boxster, but should work for all model years.

Tip Tip: When ordering wires and connectors, get a couple extra. Chances are your local Porsche parts department does not stock these items. Considering how inexpensive they, it's better to have a couple on hand in the event they are damaged or misplaced than to wait 3-4 days for a replacement.

Qty.Part NumberDescriptionCostNote
2996.618.521.00Control Unit Seat Heater (Relay)$52.47
2996.612.540.01Wiring Harness Seat Heater$26.31
2996.521.531.01Foam Part Backrest Cushion with Heating$96.30
2996.521.521.01Foam Part Seat Cushion with Heating$203.90
2996.618.531.00Support Control Unit (metal bracket)$7.73
2999.591.712.40Plastic Rivet 6,0 x12, 0$0.22
2996.613.152.00.A02Tip Switch Seat Heater$20.40A02 is color code
1999.650.109.40White Female Electrical Switch Connector Housing$2.96
1999.650.035.40Black Female Electrical Switch Connector Housing$1.88
10999.650.330.00Electrical Connector (Female spades to tip switches)$.46
3000-979-008-AElectrical Wire/Connector (Small square to seat)$2.05Audi. Cut in half to make 6.
1000-979-227Electrical Wire/Connector (female blade to fuse)$2.75Audi
1000-979-117Electrical Wire/Connector (female bullet to seat)$2.10Audi. Cut in half to make 2.
1999.650.320.22Contact Bushing (to relay BS15)$.16
1999.607.060.00White 25A Fuse

Note Note: As you can tell by the part numbers, many components are shared between the Boxster and 996. Keep this in mind if you decide to look for used parts.

Upholstery

The heating mechanism takes the form of a heater coil which is molded into the seat foam. I have heard reports of cars that have come with the seat bottom cushion and/or back containing this coil, even if the heated seat option wasn't purchased. I can not confirm or deny this. You can check for yourself by looking for two wires that protrude from each seat cushion and end in a black plastic plug. In addition you can look at the part number on the tag attached to the seat foam. It is unique to cushions with the heating element. (Part number for cushions with the heating element is listed above.) Even if your car has the cushions, you will still likely need switches, relays, wiring harnesses, etc..

Assuming that your current seats do not have the heating elements, the easiest thing to do is find a pair of heated seats and swap out the existing ones. I did not have luck finding heated seats in the color, style, and condition I needed for a reasonable price. They seem to run a few thousand dollars for a used pair, not including shipping. Places you can try on your own include eBay, salvage yards, club meets and newsletters, etc.

Upgrading the seat foam in your exising seats will likely be the most economical. While you can do the upholstery yourself, usage of hog ring pliers to remove and re-install seat cover material may be required. I did not feel comfortable doing this, and had a professional shop install these for me.

Section II: Disassembly

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