I found a decent deal on a '98 tach on Ebay. Today I finally got around to trying to add it on to our '05 Sportster. I quickly figured out that our '05 uses data link throughout, so the older non-data link tach needed a signal tap from the primary side of the coil. We did that.

So, the issue is that the tach appears to indicate about 1/2 what the engine is actually turning. We hooked the signal wire to the primary wire for the #1 cylinder on the coil...which is how it was attached on the '98 sportster it came off of. I am thinking that the '98 coil may have been a double fire for each cylinder, whereas the 2005 coil is a single fire per cylinder.

Has anyone messed with this and figured out how to wire the older tach so it indicates correctly on a newer data link bike?

 

You're right on with the double fire single fire aspect. There's no way to get it to read properly because the tach itself is programmed for dual fire. Unless it sees a dual fire signal it will read half.

 

Bummer! Do you know if there is a way internally to modify the older tach? Some form of calibration?

 

Not that I'm aware of. I believe it is part of the internal circuitry and is not capable of being changed.

 

Well, thanks. You saved me spinning my wheels trying to beat a dead dog. I spent some time on Ebay and Board Tracker and found the "correct" harness and data link type tach. I guess I can save the '98 tach as a backup for the '99 FXDX.

If it works, I'll post part numbers for those that follow. And, there is a kit for this conversion, but it is no longer marketed for the 2006 or earlier Sportsters. Not sure what changed. Likely something with anti-theft on the newer instruments.