OK so i just swapped a D16y8 in for my D15y5 and it just got runnin and all the gauges work except my tach and my spedometer...whats the deal? How do i fix this, how do i diagnose where the problem is coming from?

 

check the connection at the VSS for the speedo problem.

maybe ohm out the wires from the euc to guage cluster to make there isnt a cut in the wire somewhere.

 

this may be a really simple fix

just check all of your fuses