After searching the forum for similar issues, I created an attack plan and crossed things off the list.
Battery terminals? No... cleaned and no change.
Battery? No... Even though new, had load tested at auto store and checked out fine. Pretty sure it wasn't the issue since things like headlights and power windows functioned normally.
Body ground issues? No... weren't corroded but cleaned up connections anyway.
Alternator? No... To save time removing it, I disconnected it to make sure it wasn't loading down the electrical system. No change (with fully charged battery). Did a diode check to make sure alternator wasn't draining battery while vehicle was off, checked out fine.
Came down to one of two things.... Body Control Module (or Dashboard Interface Module as it's called in some places) or ignition switch.
Decided to go with ignition switch after reading other have had similar "no start/crank" issues and changing the ignition switch solved them. Got an ignition switch and exciter ring (BTW, eBay is a good source for new parts at good prices and free quick shipping) and swapped them out. With instruction found on a thread on this forum, I was able to pull the dash apart and swap out the switch in less than an hour. Not bad for an hour of my time and about $160 in parts.
Not only does the new switch have a much more "positive" feel when turning to the various positions, The SES (service engine soon) light illuminates and fuel pump primes immediately in the RUN position (used to be a random delay and vehicle would not start till light illuminated). From looking at the wiring diagram for ignition switch connections, I'm guessing that the part of the switch that supplies crank voltage, power to the DIM, and power to the anti-theft module went bad causing the random crank and security issues.
Which part is everyone using as a replacement ignition switch??? The switch I pulled out was marked GM #25721650. I replaced it with AC-Delco # D1431D. Is there a difference in quality/durability of these parts?
Do they go bad often that having a spare on hand is a good idea??
PS.... Disconnecting the cable going to the shifter FIRST lets you pull the switch farther into the radio opening and makes it easier releasing the two big connectors on the switch. If I had done that, I could have changed the switch in about half the time.







