View Full Version : What wire for the Speedo?

12-11-11, 06:11 PM
I have a 2005 Northstar 4.6 from a Deville I believe in a kit car. I want to hook up a speedometer and need to know which wire to conect into and were would be the best spot. I also Believe I'm using a Pontiac GXP ECM. My speedo is calibrated for a GM 18 pulse sender. Can anyone help with this?

Also my new radio with navigation is asking to be hooked up to the speed sensor wire. can I use the same wire?

Why would the radio also want to hooked up to the back up lights and parking brake?

Thank you for any help or advice!!!!


12-11-11, 06:38 PM
The transmission is where the speed sensor will be, is it a 4T80E trans ? Rear engine rear drive I'm assuming? Neat lookin ride :)

12-11-11, 08:51 PM
hmm im not usually one for kit cars but that looks really sweet

12-11-11, 09:07 PM
Thanks guys, I wasn't a kit car guy till I found this thing. It is a blast. Last owner built it, it needs gone through and refined a bit though. That has been my winter project.

It is a front wheel drive set up, Auto 4 speed.


12-11-11, 09:13 PM
Hmm, you're going to have to ID the trans for me. Behine the engine, farthest away as you look at your pic above, is the transmission. On the top of it as u look thru the hood, about 5inches behind engine, is a stamp that will say 4T80E, or possibly another identifier. you may have to lift a wire harness or take off your air induction stuff, or both... to see it.

So is that the radiator smashed against the engine (or almost at least) in right side of pic above? WOW is that close.

12-11-11, 09:37 PM
Rad is in the front of the car, it is VERY tight in there. The car is small.

I can find no stamps on the trans....

Do these pics help?




12-12-11, 08:58 AM
That looks like the 4T80E... if it is, here is a pic of where the speed sensor is (on top of the tail housing). What PCM are you using?


12-12-11, 09:52 AM
Pontiac GXP

12-12-11, 07:31 PM
Any idea what color wire would run the speedo?

12-12-11, 07:35 PM
Did the wiring harness come with engine?

12-12-11, 08:09 PM
Yes, That is all factory.

12-12-11, 08:45 PM
Do you want the PCM connector end view from the service manual? The pinout from there you can run to your gauge cluster.

12-12-11, 10:32 PM
That would be awsome!

12-13-11, 02:18 AM
Also my new radio with navigation is asking to be hooked up to the speed sensor wire. can I use the same wire?

Why would the radio also want to hooked up to the back up lights and parking brake?

If the unit also plays videos or has video input, it could use these signals to prevent you from watching a movie while driving, or to switch to video input from a backup camera if available.

12-13-11, 06:29 AM
Here are the pinouts for the 05 deville pcm

12-26-11, 09:06 PM
I really aprciate the help so far!!! But... I have chased for wires that I believe may be gone out of my harness but who knows:bonkers:. I did find the Vehicle Speed Sensor with the purple & Yellow wires coming off it. Then I read this on Autometers website:

"Most factory equipped speed sensors will operate our speedometer. If you are running a late model transmission in an early vehicle with no computer, then that is o.k. You will have two wires on most factory speed sensors. Ground the low-side signal wire and run the hi-side signal wire to the speedometer and calibrate. Itís just that easy. "

I do not know if the yellow and Purple wires are still doing anything for the ECM. Should I do as it says and ground the Low- Side and use the hi- side, should I just try and use the high side? My biggest fear is hurting the ECM.

Thanks for any input!!!!:bouncy:

12-27-11, 10:34 AM
I would think you would still need to run the speed sensor through the PCM otherwise it will set a DTC. PIN 8 on C1 of the PCM goes to the dash wiring through a large connector that is usually mounted on the driver side strut tower (in normal caddies). It should be a dark green/white striped wire.

12-27-11, 10:45 AM
All of that wiring is gone... I have searched all around the PCM for a dark green & white wire with no luck. Should I just try and tap my speedo wire into the high side and not ground the other side?

12-27-11, 01:02 PM
If you aren't concerned with setting DTCs (I do not know anything about kit cars... does the gauge cluster have a check engine light anyway?) then by all means run the wires from the VSS to your speedometer as instructed.

12-27-11, 01:07 PM
I'm gonna give it a shot! No cruise, No speedo (other than the one I want to hook up) and no check engine lights. What else would the speed sensor give info too?