The Trail Tech tach/hour meter has only one wire (sheathed in black with the red end sticking out) that you are instructed to wrap around the spark plug wire 5 wraps. It may work without wrapping if you get it close enough.... but I didn't try that.
The wire is about 4 feet (over a meter) in length. You can cut it to any convenient length and coil it up a bit like I did (I can move it from saw to saw for carb tuning each) under the top cover.
My only complaint with it is the battery is sealed up in potting resin (claimed to last 5 years), so when the battery eventually goes dead I'll have to work a bit harder to replace it.
Its cheap and works great though. Hope this helps.