So I installed my Z1 today in my 2004 GMC Sierra Crew Cab. I got Ducati's bypass installed and that seems to be working properly.

2 Problems I'm having:
1) Where the heck is the VSS wire? I've searched and can't find it, I've even looked through the factory service manual for the truck and can't find anything for a VSS other than a connection at the transmission. I can't imagine I really need to run a wire to the rear of the tranny to hook up the VSS. Does someone know where I can get the VSS connection in this truck?

2) The age old dimmer on a GM vehicle issue. So I don't have the extra connector for a factory nav system like someone suggested and I've probed every wire in the headlight switch and the only wires in the switch that change voltage are +12V when the lights are OFF and 0V when the lights are on, I'm assuming I need +12V when the lights are on since the Z1 is always in night mode on the maps if I tap into any of the leads on the headlight switch that change voltage. Anyone know where I can pull a switched 0V with lights off to 12V with lights on lead on this truck? I've tried the headlight and parking light signal wires off of the BCM but even those don't give me 0V when the lights are off.

I'm happy with how the install went, I'd just love to figure out how to get the VSS and the Headlight wire connected for Day / Night mode without having to use a relay or a seperate switch.

Thanks in advance to anyone that can help me figure this out.

Ralph

Well, if you found 12V off and 0v when on you can do a relay to "inverse that wire". But did you find a wire that was more like 6V on and 0v off? Or maybe 8V on? The dimmer wire will be a pulsed modulated signal which will register like 6V when the lights are on. My circuit will work off that as well. I don't know anything about your particular vehicle myself, but with all your probing, did you find a wire voltage like I described? You can tell cause when you adjust the brightness of the lights inside, that voltage will change. You can use that.

I found a 5v dimmer wire, but it's always 5 volts it never goes to 0v when the lights are off. Don't know if that's because of the automatice headlights or the funky switch that GM uses for the headlights. So I did find the 5v dimmer wire, but it doesn't seem to work for managing the day / night mode of the Z1.

I'll keep poking around, if nothing else I have an appointment with a buddy of mine that's an installer at a local shop and I can have him just hook up both the illumination and vss wires on Wednesday, but on the other hand it's frustrated me enough that I'd prefer to figure it out on my own.

No it should go off when the lights are off. If you have something that's 0v when the lights are off and your meter measures something from 5v-10V when the lights are on and the voltage changes based on the dimmer setting, you can use that with my circuit, I don't know about the Z1 directly. But what you found doesn't seem to be the thing to tap off of. Hope your installer hooks you up (pun intended).

Speed Sense dk. green/white 4K instrument cluster, pin A4 or PCM
The PCM (Powertrain Control Module) is in the left front of the engine compartment to the left of the fan shroud. The VSS wire is in the green plug, pin 50.
It is much easier to get it at the cluster than the PCM
Keith

Well, Keith is right for more than the obvious reason...

I thought I'd run the VSS wire from the PCM, through the firewall, and over to my Z1 under the dash. I thought it would be easier than grabbing the wire at the instrument cluster, until I studied the cluster *4 screws and one 24 pin connector.

(Obviously I did this step before I took the dash apart to see how easy it would be)

That worked great, UNTIL the Z1 complained that the speed signal was "irregular". After a little tinkering with no luck, I decided to give a try to taking the VSS signal from the cluster.

Somehow, the signal from the PCM under the hood is different from the signal the Z1 gets from the cluster. Now everything works great!

Moral: use the dark green/white lead A4 from the cluster.

I guess the shorter the lead from the VSS wire to the Z1, the better the signal? Most likely, the truck re-processes the signal from the PCM, and sends it to the cluster in the format that the speedo needle needs to show the right speed.

Speed Sense dk. green/white 4K instrument cluster, pin A4 or PCM
The PCM (Powertrain Control Module) is in the left front of the engine compartment to the left of the fan shroud. The VSS wire is in the green plug, pin 50.
It is much easier to get it at the cluster than the PCM
Keith