The problem could be a shorted park netual safety switch . Do you know what a wiring diagram is ? It shows all the componets involved in a electrical circuit ! You IGN.1 fuse 40amp , GM calls it IGN A fuse 40 amp . It feeds the ignition switch and pin 30 at the starter enable relay .When you turn the key to the start position it sends B+ voltage to #8 crank fuse , located in the I/P fuse box ,from there it goes to the park netual safety switch , to pin 86 or 85 of the starter enable relay ! If you pull the relay out of the fuse box an look on the bottom you will see this four set's of numbers ,30,87 & 85 ,86 You can test at the fuse box where the relay plugs in . Here is a video on how to test . The guy presenting the video uses a horn circuit , but it works the same way . It happens a lot , the park netual safety switch shorting out . It may or may not be the problem .
VEHICLE RELAYS Operation Diagnosis
Here is a web site for free wiring diagrams
http://www.bbbind.com/free_tsb.html Enter your vehicle info . then under system click on engine , then under subsystem click on starting . Then click on the search button an a link will pop up , click on it .You will see all the componets , connections , wiring colors etc... for the starter circuit for your vehicle .
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