Once you knew what signal your existing tach is needing, and once you know the signal type from the new ECM, it could be as simple as purchasing a tach signal adapter from a manufacturer such as MSD, Autometer or others.

 

So how do i findout what signal it needs?

 

And its an 04 tahoe ecu

 

so are you saying that u spliced the white tach wire and ran it to your 93 gauge panel? or did u run it to a 99-newer gauge cluster? If it is hooked up to your 93 gauge cluster, it might be wrong signal pulse or something.

I just installed a 5" tach. And u do have to run the tach on a 4 cyl. pulse for it to work right.