my 2000 blazer is not shifting from 1st to 2nd, or 3rd to 4th. codes are reading p0740,p0753,p0758,p0785,p1860. from reading and knowledge of GM's faulty ignition systems; i assume its my ignition switch not giving the proper voltage to tcc. Also have a driver window out, cruise control, left turn signal flashes like a bulb is out but it isnt. do these all relate? plus the radio is aftermarket but was installed by the last owner. could its installation change the current to tcc since the door fuse box shows radio and ignition sharing a fuse?

 

Are you able to shift the trans manually?
My suggestion is to check the various electrical chassis connections, battery cable connections, dash ground connections, etc.
Disconnect the radio power at the radio to eliminate it being a problem.

 

With the ignition in the RUN position, check all fuses with a volt meter or test light. Do not remove the fuses, probe the terminals on top of each fuse. Both terminals must show battery voltage.

Check the electrical connector going into the trans. Round, grey plug, maybe 1.5" in diameter. Passenger side, just above the pan. The plug goes straight down into the trans. Unplug it, clean it out with brake clean, etc, blow it out with compressed air, push it back in until you feel it "click" into position.

 

I used a test light but removed #24 fuse and probed the top prong and it was lit in all positions and driving thru gears which i can manually change. i turned the radio off to do this but can unplug when i take dash apart to look at ignition switch. my test light is 6v-12v so whippin out my meter. if i mess with testing my switch, will i need to relearn the passlock cylinder? also my driver window just started working again. no other changes.

 

To check the ignition switch, all you need to remove is the lower column cover, and the cover above the brake pedal. "No" on the Passlock relearn. The sensor behind the ignition lock cylinder reads the key and sends the data to the BCM. All Passlock data is stored in the BCM. If an authorized key is not being used, the BCM will not allow the PCM to fire the injectors.