I have a 2008 Sportster Custom. I have the HD tach kit that is correct for my bike. I found the wires coming out of the speedometer and hooked them up correctly to the orange/white wire for 12V, the black wire for ground and the light green/violet wire for the serial data signal. When I turn on the ignition key, the light comes on and the tach needle immediately becomes erratic and jumps all over the place up to around 2K RPM. When I start the bike, it continues to be erratic and is not responsive to increasing the revs. I redid the datalink connection and feel I have a good connection. I also ran a ground wire directly to the battery. After reading one other post, I found the correct data link wire at the ECM and tapped into it there. Same results. I am a newbie to this bike but I am not a newbie when it comes to wiring and have installed many electrical components during my too many years, including tachs on other bikes. I am befuddled!!!

 

Sounds like you have the install dialed. I wonder if the unit itself is defective? Maybe the dealer could cough up a new one.

 

+1. It IS a HD Tach?? That is weird. Im drawing a blank also, I'd have the stealer swap it out.

 

It is a HD tach. I bought it from an individual but it had never been installed. A number of sites I visited said that the light green/purple serial databus wire is the correct signal. However, the instructions do say to hook it up to the number 3 pin on the speedometer plug. My Clymer wiring diagram does not show any wires going to the pin. However, I did come across another thread where the guy used that pin and it worked. Before I do anything else, I am going to call the dealership and ask them where to get the signal.

 

I purchased a Hd tach for my 08 sportster. According to the 08 cat. It was the right part #. The dealer said it was not. I had to pay more, but the new tach has a shift light.

 

I talked to the dealer this morning. He said I need to pick up that light green/violet wire near the coil pack. I will try that and see what happens.

 

Well the dealer was wrong. In his self-defense, his guy who was familiar with the wiring was not at work yesterday.

There would have been no problem if I had followed the HD instructions. They called for installing wire to a pin at pin #3 on the back of the speedometer. The only reason I did not do that originally was that my wiring diagram did not show any thing going to that pin, plus I had seen a number of posts saying to use the light green/violet serial data wire. I read another post where a guy had the same problem as me, called HD and was told to install a pin there and it would work.

Since I did not have the correct pins for the plug, I went to the dealership to first discuss this and then to get the pin. He got out the HD wiring diagrams which also did not show anything going to that pin. Since he wasn't sure, I decided to get some pins (Only needed one but I knew if I only got one, I would mess the first one up. I did!) and install it. Fortunately, my repair manual showed how to install the pins. I hooked everything up, started and it and, voila, it worked!!

This just goes to show that you cannot always trust web site info. At least on my bike, that did not work.

So, all is well. I also installed a headlight modulator to flash the headlight as I go down the road. Hopefully, it will help someone see me better.

 

The speedo is the sending unit for the tach signal since 2004, Glad it worked out.