factory tach

[clemdaddy]

i have a couple of factory tachs and they're not reading right. seem to be in hundreds instead of thousands. is there a converter that i'm missing? i remember the old sun tach needed a transmitter box that you mounted on the firewall. and i've gotten aftermarket tachs for these trucks but they don't seem to have that problem.

any help would be appreciated. maybe there a small converter that could be hidden under the dash. don't know...