Tach install 96 Ram help

Installing an aftermarket Faze tach on my sons' 96 1500 5.2. It has a factory tach in dash but he wants to hook up one Santa brought him...need to locate the tach sending terminal, I hate to cut into the coil wires or mess with the dash cluster, I figure there has to be a diagnostic port or something that will have the signal we need.. Where would I pick up the - signal fom the coil pack? Thanks.

this may help,
http://www.dodgeforum.com/m_413705/tm.htm
i dont think there is a dignostic port but i would make aa connector that can go inbetween the coil connector and coil to not cut the wire then it could piggy back off it