Changing to the 180 mph cluster...
 

Both my tach and my speedo sometimes stop working and i have to tap it to work. Also my voltage is always at 12v plus the 3/4 fuel. Is also this fround a bad ground or the guage cluster???

Is it possible to intall the 180 mph speedo to can that had the 160 and get an accurate reading?????

Have you re-seated the connectors going into the cluster and cleaned the ground behind the cluster? That seems to fix most issue like that. I tend to slather some dielectric grease on there as well.