I bought this 98 f150 4.2 V6 used couple days ago. It had an aftermarket tach mounted in it. It was functioning but not properly....like it wouldnt go past 2500. They connected the signal wire to blue wire by the coil packs. I did some looking on here and apparently it should be connected to white/pink wire from computer behind battery. So I tried that and the tach completely quit....so I tried another working tach and apparently fried that one too. What is going on with this thing.....do I need a special tach?

 

You could always check out a junkyard for a 97-98 gauge cluster with a tach in it. Just make sure the odometer is the old style analog not the newer LED and it should be just a straight plug'n'play swap. That's what I did to get a tach in my 97.