First do you have a voltage meter?
If you do follow these steps:
Remove the gauge lighting from the circuit you tapped them into.
Replace the fuse with the SAME SIZE fuse. Never increase the fuse size. Its sized to protect the wire from overheating and burning down tour truck.
Pull the dash forward at the headlight switch. Using a meter find the dimmer wire on the back of the headlight switch for the instrument lights. You can find it by adjusting the dimmer and seeing a change in voltage.
Tap this wire and you will be fine, mine has been for 6 years now with three gauges.
This will also let you dim the gauge lights with the dash lights.