Installing a Horizon P-1000 tachometer
From Bondline
Bluejay Adametz contributed this account of his installation of an electronic tach in his '79 Tiger:
I just replaced my old mechanical tachometer with a shiny new Horizon Instruments P-1000 digital tach. Aside from the usual poor accuracy of mechanical tachs, my old tach had a tendency to become unstable, the needle bouncing +/-200 RPM at times.
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Certification
The P-1000 is STC'd as a replacement for our mechanical tachs, so the paperwork is minimal: log book entry and 337 approved by an IA.
Ordering
I ordered mine directly from Horizon Instruments and it shipped the same day. When ordering be prepared to provide all the specifics of the aircraft: make, model, serial number, N-number, owner, and engine model number. Horizon can set the hour meter on the new tach to match your old one if desired, so have that number handy as well. I had my airplane down for annual at the time, so it made sense to match the meter readings and avoid more math going forward.
In the box
The package came with almost everything needed, including a circuit breaker, wiring harness, and paperwork. The only parts I added were a bit of wire and crimp terminals (see below). The supplied breaker label didn't match my decor (white on black), so I made my own label.
Installation
I thought about removing the old tach cable housing intact, but after noticing all the other wires and cables going through that hole, I decided to just cut it and remove the pieces. I considered myself committed at this point.
The installation was straightforward, and followed the supplied installation instructions. The only thing I had to work at was getting the circuit breaker installed, since the supplied breaker is a different size and configuration than the original breakers. I have room where the original factory breakers were installed on my 1979 Tiger, but I could not obtain a 1-amp breaker in that form factor. I ended up mounting the Horizon-supplied breaker there, and used a short bit of wire to connect it to the bus:
On further consideration, it's probably not a bad idea to have a pullable breaker there, as anything that displays a version number as it "boots up" just might have to be rebooted at some point, and this provides an option to do just that should that seem like the thing to do.
The instructions say to not cut the mag wires. I was concerned that the extra wire under there might cause some interference in the audio system, but none was observed when the system was tested.
Seal up the firewall:
And, power on!
Don't forget to label the breaker.
Operation
On run-up the tach performed as advertised, although the 1-RPM resolution seems to make it appear a bit jumpy. I think we were seeing RPM changes just from the wind that wouldn't be noticed on a mechanical tach. The mag drop function takes all the guesswork out of mag checks.
Flying with a digital tach takes a little getting used to: reading a number is just different from a needle pointing at a line on a gauge. Since those numbers have a 1 RPM resolution, they tend to move around a lot, usually +/- 20 RPM in not-all-together-smooth air. After getting used to this different thing in the panel, I went back to using it the same way I used the analog tach: to set and monitor power settings. The red light will get your attention in a manner that a needle pointing to a red line won't.
