Problem with wire signal

I have a tach signal wire coming from my Dyna 2000

It is wired to my tach, signal wire and works very good.......... but when I connected my WEGO AFR tach signal wire to the same location, the tach stops working???????

below is how I have it connected now.

I think the fix might be to install a diode or something that makes the second signal wire a one way only. So the signal goes out but cant come back to influence the tach?

I hope this makes some sense.

Find the resident "Wizard" Loudhvx, he should be able to help you. I agree, a Diode is probably needed, but what size?

With some testing, it's possible to come up with a simple circuit that should allow both tachs to work, but why can't you run one off the Dyna 2000 wire, and the other off the coil wire?

You are correct, but the coil connection is very noisy for electrical items and makes the tach a bit jumpy....like it just had 10 shots of espresso.

the digital signal from the dyna 2000 is crystal clean, my tach action is super smooth. I'm able to get a quality tach graph for the first time from my WEGO.

The other issue came about with the WEGO AFR data logger and the Dyna - S.

The AFR part worked great, but even with extensive Daytona Sensors tech help.......we never achieve a tach graph that was lendable.

My tach and WEGO are working, just not together.

The Dyna S has a super short fire time (and super long dwell). That would probably explain the tach issues with that.

Well, the first step, then is to confirm the WEGO works with the Dyna 2000 (with the other tach disconnected).

Next is to disconnect all three, and measure the voltage on each wire with the ignition on, but the motor not running.

Then connect the tach to the dyna 2000 wire, and measure the voltage at the junction.
Then disconnect that, and do the same measurement using the WEGO connected to the 2000.

All measurements done using the battery negative post as the reference (black meter lead).

Normally a tach signal would be a pull-down signal, but sometimes it will have it's own internal pull-up. Usually the tach wire has it's own pull-up as well.
If one tach wire does not have a pull-up, and expects to be connected to the coil wire, which would do the pull-up, it may pull down the other tach. That's one possible scenario that would cause the symptom you are seeing.