installing a tach in my 97 mercury grand marquis
 

I know that the car has multiple coil packs but when installing a tach do I have to hook it up to all packs ? and if so which wire is the ground ?

I could really use a hand

I know this is old, but I'm looking for the same thing man. I saw a video on youtube using a Lincoln Town Car and it showed a large coil pack in front area of the engine, had 2 wires coming out one side, one on the other. The single one was green and is that actual tach wire, he said just to splice it in there. I'm doing my installation in my '96 tomorrow. Wish me luck, and good luck to you sir

How did it go?