i don't know much about installing an alarm system in a car. what i do know is that there is an obscene amount of electrical tape, tie wraps, and connections that were not done correctly under my dashboard. The original reason i opened it up was to fix a loose connection that was making the gear select and odometer led display flicker. which i did, but i noticed some other wires and a couple of small toggle switches and went digging... wow, lots of tape... it seems the alarm has been disabled by removing the inline fuse. what of the other connections? check engine light is and has been on. low voltage bank 1 sensor 1. changed o2 sensors in bank 1 and 2 and had the code cleared, same one came back. Changed the fuel filter, same code. The truck will intermittently drive fine and then barely at all. changed the alternator to get it out of the guys drive way, going to replace the battery tomorrow. but this went from bad to worse, after taking the dash apart and looking at everything it will crank but not start. even before, i had some starting issues cold and hot. wants to go but won't, let it sit for a sec, starts right up. not anymore, even with cables and the engine at 3000 on the other side it won't turn over. any insight would be appreciated. sorry for the length, i just want to be thorough.

 

After looking at what it would take to install one I paid the price for installation.
They're complex. Even with your lengthy post there's not enough information to begin diagnosing.
I'm guessing that unit is both an alarm and a remote start. On our Blazers there's what's known as a Passlock system. In the lock cylinder is a sensor that measures resistance of the key & if it doesn't match what's stored in the computer, it won't activate the fuel pump. Get a new key made somewhere and try to start the truck with it and you'll run into this, the blank key is made of a slightly different metal. A signature of this problem would be the truck wants to start for a second then quits trying. How this affects you is when you install a remote starter you also have to install a bypass in the Passlock wiring because the remote start has a different "signature" than a proper key. Not putting the bypass in can result in the truck starting with the remote but not the key.
Sometimes the computer loses its memory of the Passlock "code" (I've had this happen to me with a connection the requires wiggling).
Hopefully you didn't move any of those toggle switches, one might be a manual fuel pump shut-off that someone might hide somewhere for extra security.
Try this to make the computer relearn the Passlock code.
1. Place the ignition key in the on position
2. Try to start the truck. The truck will attempt to start and stall. Leave the key in the on position.
(if it didn't try to start ignore the rest, you have a different problem)
3. Wait 10 minutes. Watch the SECURITY light. It'll flash for a few seconds and remain on for 10 more minutes.
4. Turn the key to the off position after the security light goes out. Wait at least 30 seconds.
Perform steps 2-4 two more times. It should start the next time you try it.

 

I'm a little confused.. why did you change the 02 sensor and fuel filter if you are dealing with an alarm? Perhaps I'm not clearly understanding your post but are you thinking that the alarm is causing the SES light?

 

Sorry, should have clarified that. I was too busy wondering where to begin with what I wanted to say. I'm dealing with the SES and codes as separate issues from the non-start. As I said, even with all the info she gave us it's still not enough.
I made numerous assumptions and actually rereading her last sentence I'm dead wrong. I thought the truck turned over but wouldn't start, I see now it won't even turn over. I was hoping the unit under the dash was keeping her from starting it and the other issues could be dealt with once the truck was running. I just know I've sat in a non-starting truck because I had a connection "cheese out" on my remote start and when she spoke of than unit... um... I lost focus on the WHOLE post. O2 sensors wouldn't keep it from starting anyhow.