i have a 91 ranger four cylinder manual. it didnt have a tach when i bought it so i bought a replcement used cluster with a tach. well i got it plugged up and put in but when i start the engine the tach reads about 500rpm idle and never goes past about 1000 while driving. what could be wrong with it and how do i fix it?

 

Did you turn the little screw on the back of the tach to the other setting, it probably came out of a v-6 truck and needs to be set to 4 cylinders.

 

So as a stock tach it will have that adjustment? Someone told me only aftermarkets have the selectors

 

Negative, the stock tach has a small green adjustment switch on the back, you need a small flat blade screw driver to change it over from 6 to 4, it is NOT marked just move it to the other setting if it came from a 6 cyl Ranger.
I did this recently on my 93 2.3 Splash which came with no tach, took a cluster from a 94 4.0 v-6, moved the switch, installed and tach runs like a charm.