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I need to know how to wire up my 73 Ducati sport Tacho.

There are 4 wires in the loom, I have a spare white wire that goes nowhere. Rather than go like a bull at a gate, I thought I might ask.

Thanks Gum

PS someone must know

I posted this in your pic thread as well.

Finding a wiring diagram with the electronic tach is difficult (non existant?).
How have you got it wired now? What color wires and where do you have them attached? That might help.
You need two for the light, and one to transmit an exciter voltage from a coil and one to ground to complete the circuit.
The light should be easy. All of the instrument lights will use the same two wires. A diagram would be useful, eh!
On the wiring loom near the branch for the coil wiring is a single red wire, this is the feed to the tachometer. At least it is on a '72 GT.
Think of the tach as a volt meter. The needle moves relative to the number of voltage pulses from the coil. The faster the pulses the higher the needle moves.
Keep in mind, too, that most owners binned the electronic tach in favor of a mechanical one because the movement in the electronic tach was delicate and prone to self destructing from vibration
Dean