Installed new starter on 1999 chevy tahoe 5.7 and it tries to start without using the key

ONE OF THE WIRES ON THE STARTER IS ON THE WRONG TERMINAL. OR TWO OF THE SMALL WIRES ARE MAKING CONTACT WITH EACH OTHER. CHECK OUT ALL THE WIRES. HOPE THIS HELPS YOU. PLEASE KEEP ME POSTED. THANKS FOR AN HONEST RATING AND FOR USING FIX-YA. GOOD LUCK

First check to see if you are getting power to signal wire at starter without the key on if no power to signal wire check to make sure that there is not a short between main battery cable and signal terminal if ok suspect faulty starter solenoid if you have power to signal wire without the key being turned on could be short in wiring or bad ignition switch if this is the case you sould get wiring diagram for proper wires to test

Your power wires that go to the starter are touching together as soon as you plug in the battery the car wants to start. Go under the truck and check that the wires are not touching each other when you tighten the wires they tend to turn and touch its a common mistake.Good Luck