I just got done installing the Custom Tach (side by side bracket with speedo) from HD on my Sport. I followed Bert's excellent instructions and everything seemed to work well. After riding around 50 miles, the tach needle started jumping all over when the engine hit 3K. Now it seems totally messed up other then at idle. The power is fine to it as the light is on and doesn't flicker or anything. The speedo is fine and the needle is rock solid, along with the light not flickering or anything.
I pulled everything apart and visually double-checked the wiring and grounds. Everything seems fine.
Does this sound like a bad tach, or a problem with ground somewhere other than the harness under the riser cover? Does the tach lead come from the coil on this bike?
All indicator lights work fine and there doesn't seem to be any other problems with the bike.
I bought the tach kit from Surdyke HD on eBay. It was brand new in the shrink wrap.

Any help would be greatly appreciated!!

Dude, I put one on my '02 883 and also had problems. Found out it was my own damn fauilt. Bert hooked me up with his digital photos. My guess is its not the tach. The connections are critical. Make sure you didn't reverse the wires (like I did) inside the harness that you have to assemble. The one that plugs into the back of the assembly? Also make sure your made good connections inside that deutsch connector under your seat. You'll find it. I did....

Thing is, I followed Bert's instructions from the start. I didn't do anything with connections under the seat. Was that something that was in the Tachometer instructions? I actually never even looked at them. I just had my laptop out in the garage with Bert's directions and I followed them step by step. The tach worked initially. It stopped after 50 miles or so. I am wondering if I might have a bad ignition coil and the tach is just showing it before it actually fails altogether.

There is no deutsche connection settings under the seat for the 02 Customs. If the tach worked okay for 50 miles then it sounds to me as if the tach has gone bad.

I pulled the whole thing apart, re-did all the connectors, re-wrapped all the wires and put it back together. I have ridden it about 10 miles (due to the disgusting weather here in SE PA) and it seems to be working fine. I guess maybe one of the ground wires was in a place it didn't like? Would a ground problem cause the tach to misbehave, yet the backlight stay on without flickering or anything? The speedo didn't seem to have any issues either. Well, at least it seems the tach is OK. Surdykes said it would take the tach back and send a replacement, which is cool

Thanks for the feedback I got.