Choosing the tacho output
A tachometer counts pulses. Many gauges, especially factory ones, need each pulse to swing up to a real voltage, not just float when the output switches off. That's why the Nexus asks for an output with an active pull-up for the tacho signal. An output that can only pull to ground won't give most tachs a clean signal on its own.
In the Tacho Output field, pick an output that offers active pull-up. If you can't spare one, or the gauge still misbehaves, Haltech's tacho output adaptor is made for this job.
Active State
| Setting | Output pin when the signal is on | Output pin when the signal is off |
|---|---|---|
| Low (default) | Grounded | Not grounded |
| High | Not grounded | Grounded |
We leave it on Low for almost every gauge. Only switch to High if the gauge or interface you're driving is known to need the inverted signal.
If the tach reads wrong
- No movement: wrong output selected, output has no active pull-up, or the tach isn't powered.
- Reads double or half: usually a pulse count issue. Check Pulses Per Cycle in the Tacho function, which normally matches the cylinder count.
- Jumpy needle: noise on the signal wire or a poor ground at the gauge.
