I bought one of those inexpensive LED tachometers off eBay but it didn't come with any wiring instructions or diagrams. Can't expect much for $9 I guess. After searching a bit I found some basic info on the probe wires and tach terminals. I've attached a diagram of how I believe it's supposed to be wired. What I found for the probe is the brown wire is 12 vdc+, the blue wire is 12 vdc-, and the black wire is signal. The tach has five terminals and what little info I found is terminal 1 is signal input, terminal 2 is signal ground, terminal 3 is NC, terminal 4 is input voltage "+", and terminal 5 is is input voltage "-". In my diagram the black probe wire is connected to terminal 1 (signal input), the blue probe wire is connected to terminal 2 (signal ground), and the brown probe wire is connected to terminal 3 (NC). The 12 vdc power supply is connected as shown. I'm still working on the installation so I haven't tested anything yet to see if it will work. Not sure if my wiring is incorrect if it will smoke the tach. Let me know what you think. Tom S.