I recently installed a Dakota Digital electronic speedometer on my 2010 Road King Classic. The bike already had a separate HD tachometer installed, getting its tach signal from the HD stock speedo terminal #3.

On these bikes the tach signal is available on at the HD speedo terminal #3.

The HD speedo receives the "serial data signal" at its terminal #2 from the ECM terminal # 69. The "serial data signal" is an combined MPH/RPM signal produced in the ECM and sent to the speedo. The HD speedo has internal circuitry that decombines the signals, and sends the tach signal to HD speedo terminal #3 for use by an add-on tach.

Because the Dakota speedo has a built-in tach, its terminal #3 has no internal connection. Thus, the tach signal in NOT available there. The same is true of HD's speedo/tach combos.

Connecting the tach's pink signal input wire directly to the speedo's serial data terminal #2 produces a weird display on the tach, but it's not the RPMs, so that doesn't work.

I can get the tach to display 1/2 the RPM's by connecting the tach signal input wire to either of the two ignition coils at the ECM terminals #53 (rear coil) or #54 (front coil).

If I use a jumper to connect #53 & #54 together for the dual signal, the tach will display the correct RPMs, but the bike will not accelerate correctly. So I can't do that, because both coils' firing signals are interfering with each other.

To separate the two coil signals above, I fabricated a "dual fire adapter" in accordance with the circuit plan at http://www.gadgetjq.com/tach_install.htm . It's simply two diodes and two resisters connected to isolate the two coil signals from each other, but not from the tach.

Unfortunately, it only works with either coil connected (displaying 1/2 the actual RPMs), but with both connected, the tach reads zero.

So far the only things I HAVEN'T tried yet are:

1. a Kuryakyn-made "tach dual fire adapter" available at CruiserCustomizing.com, which probably won't work anyway, or

2. breaking open the stock HD speedometer and using its "serial data signal decombining circuitry" to produce a tach signal. I need to keep the separate tach installed.

Before I do either, can anyone PLEASE HELP me to either find a tach signal for the separate tach, or double the signal available from either coil...or ANY other solution??

Sorry this is so long, but I wanted to make sure it was clear. Thanks for any assistance!

 

After posting this yesterday I stumbled upon a Kawasaki forum in which someone described the same problem trying to install a Harley Davidson tach on his Kawasaki. He built the the diode circuit noted above to provide input from each coil, but he could only get one input to work at a time. Connecting both to the circuit resulted in no reading at all, matching my results.

He was advised to reverse the polarity of the two diodes in the circuit. He did so and the tach worked perfectly.

I tried the same thing and, yep, MY tach worked perfectly. Thus, I'm sharing this on here so that anyone checking this problem out will be able to also use the solution I found.

If you're installing an HD tach on a bike that already has an aftermarket speedo/tach combo (rendering terminal #3 on the speedo useless), or on a non-HD bike with a non-HD speedo, you can still have the additional tach operate normally.

Just build the diode circuit as listed above, but reverse both diodes' polarity from the the polarity shown in the downloaded diagram. It should work perfectly.

 

I may be wrong but can't you also tap into the rpm wire on the diagnostic plug to do this. I think it is the green /brown or brown/ green wire?

 

Actually, the wire you speak of is actually a serial data signal connection like the one going to the speedo, with combined RPM/MPH data, so you end up in the same place as described above at the speedo...no de-combined RPM signal available to you unless you're using the stock speedo.

Good thought, though. Dunno why HD didn't include circuitry somewhere (besides inside the stock speedo) where one could access the DE-combined RPM signal independent of the stock speedo.