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Where is the speedometer wire?

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  • Admin

The reverse signal wire is under the drivers seat (see diagram). Look for a spot weld with several BK/BL wires. These wires are the reverse gear signal. You will need to splice into any one of these wires and then insulate (tape) well. They recommend running the wire from the Nav through the side panel and up the A pillar -- but I know folks that have run it up the center console.


Speedometer A signal is the speed from the instrument cluster. It is the same signal used for the PSE. The easiest place to get this is Relay Support 1 (the relay panel down by your left foot), Position 23 (bottom row, first relay on the left), Bridge Support Connector 1. The Speedometer A signal is the GR/PK wire.




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Wow for the life of me I couldn't get the relay panel out... it seems the left side is locked in somehow, Toolpants whats the trick on that one?

Loren the picture from under the seat, I assume thats coming from the main box under the seat, not the wiring harness that are mounted to the seat.. the only way to get that box is to pull the drivers seat out? All for a reverse wire... hmmm Any thoughts guys?

Box under the seat..


Edited by Kevin M.
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  • Admin

Relay Box --

1) Remove the fuse panel cover and the carpet cover itself by removing four screws. Release the relay carrier above the fuse panel by releasing a clip on the left and a 10mm nut on the right.

2) Pull it down so you can rotate it around to see the back.

The seat comes out easily if you have the E12 External Torx socket -- 4 bolts. Don't forget to disconnect the battery -- just in case.

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  • Moderators

For the speedometer signal you can use the gray wire with a pink stripe that is in the connector to the back of the oem radio. It is used for GAL.

There is an unused reverse signal wire under the drivers seat next to the control box. It is black with a blue stripe. You are going to have to move the wires around and remove some tape to find it. It is a stub of a wire going nowhere with a black plastic cap on the end.


If you want to remove the relay tray. Remove the 10mm bolt on the right side. The left side is held in place with a plastic lever that you push on. Get a light up in there and you will see it.


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I just put in a traffic pro. I was going to do the reverse wire like you but decided to leave it for another day in the end.

I have not noticed any problem with the sat nav despite this ommisssion. I really dont think I will bother with the reverse signal now.

Hope this makes it a bit easier for you to decide :)

Good Luck with the install

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  • 5 months later...

In my 2000 C2 Cab, the speedo A wire was already in the CDR-220 head connector wire loom. This connector is the ISO connector that clicks into the head unit. It was already there for me in the loom ;)

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Loren, Toolpants,

For a 2002 with PCM, would it be the same Grey/Pink wire that carried the speedometer info?

Do I have to unscrew/remove the PCM unit to get to it?

I am installing a Bahntech Top Control module and would like to tap into the speedo wire to prevent top from operating > 25mph.

Also, how do I disable the parking brake requirement for the top?

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  • Moderators

According to the wiring diagram there is a black 26 pin connector on the back of the PCM unit. Position 24 is the speed signal wire which is grey with a pink stripe. You hook the blue wire from the Bahntech to the grey/pink wire.

I do not think you can get to the wire without removing the PCM unit.

I know how to defeat the parking brake requirement on a Boxster, not a 996. See if Loren has an idea for a 996. There was a thread some time ago about grounding a wire from the top control unit.

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