1999 firebird V-6 intermittently will not start with good battery,connections and starter.WHY???

....when it intermittently does not start - no clicking from solenoid/starter and no 12volt signal to solenoid. but intermittently it will get 12v and start just fine.

You're going to have to trace the harness, I'm afraid. There are two connectors between the ignition harness and the BCM, one or both of them might be loose. I've seen similar issues after someone has installed an aftermarket stereo or capacitor. The harness runs right in that area. These cars are notorious for poorly manufactured BCM's. You can get one for about $150. It's located under the dash behind the glove box compartment, not that hard to get to. Good luck!

Thx! you called it! one of the connectors that plugs into bottom of BCM was loose. Removing the bottom panel under glove box allowed easy access and view. I believe hitting a pothole was the cause of connector loose. I believe my BCM is defective for horn, but not for starting system.

there ya go

For people with a similar issue and replacing the BCM didnt fix the problem, It could be the Key reader in the ignition lock cylinder starting to go bad, or the ignition switch itself.

Check the neutral safety switch if you have an automatic/clutch safety switch if you have a manual, before replacing the BCM, it might save you alot of time and money.

If your car will start with the key but dies immediately, its probably the fuel pressure regulator, or Throttle position sensor.