> From:    joel walker <jwalker17@EARTHLINK.NET>
> Date:    Mon, 21 May 2007 13:12:58 -0500
>
> [Re: tach hookup] anyway, i only needed three wires ....
> power from the dash lights to illuminate the tach at night.
> ground to the chassis for the illumination light.
> and a signal wire from the #1 terminal on the ignition coil.
>
> [...] not sure what your 4th connector would be, though ...

Some tachs only need the signal from the coil and ground - they operate
off of the juice from the coil.  Others also need +12 V because there is
a little amplifier/signal conditioner circuit in them.  This +12 V line
doesn't take much current - most likely less than an amp - and should be
hot-in-run, aka circuit 15.  +12 V for tach, +12 V for lamp, signal, and
ground would be four connections.

Matt Roberds