Battery powered engine tachometers, like this Tiny-Tach TT2A, have just two connections: one ground wire and one spark “pickup” wire.
The white wire attaches to engine ground.
Wrap the red wire around the spark plug wire. Depending on the strength of your engine’s ignition, you may need to adjust the number of wraps.
Thanks for the thorough guide – just ordered up the bracket and the Tiny Tach as I thought this was an elegant installation. Where is the engine ground located?