When I had my Zetec MTX tour... I also didnt have a tach in the cluster... I thought it was odd, and hated it... My brother bought me a Sunpro 2 tach from Autozone... just an el-cheap-o one that had a white face (To match my overlays). I set it up so it hung down into the cluster to the left... Looked classy, everybody I knew liked the look of it right there... But upon install I never had a problem with the needle rapidly bouncing... I mean, the zetec in that particular year is famious for having a cycleing idle that bounces between 700 and 900 rpm's. So I guess I dont exactly know what your problem is... You might have a bad gauge...
when I hooked up my signal wire I had to run it to the engine bay, all the way across to the passenger side to a big cluster of wires, I dont recall which wire it was we spliced into... I could check my install book... But I never had any problems with signal...
