1999 blazer, which method do I use to reprogram a keyless remote, ground the keyless programming connector to ground or cycle the ignition switch while holding door switch and hold lock and unlock button on transmitter? Also the remote is from another vehicle, does this matter? thanks

 

I have the same year Blazer and here's how I did mine. These instructions are from http://www.programyourremote.com/
Yes it does matter what vehicle the transmitter is from because there is more than one system. If it's from the same year Blazer it will work but other than that I'm not sure how to tell the difference and you didn't say what vehicle the new transmitter is from. I know there are a few more that will work so hopefully someone else will know.
1. Close all vehicle doors. 2. Insert the key into the ignition. 3. Hold down the power UNLOCK button on the driver’s door panel-continue to hold down until instructed to release. 4. Perform steps 5 through 8 in fairly rapid succession. 5. Turn the ignition switch to the ON position (as far as you can go without starting the engine). 6. Turn the ignition switch to the OFF position. 7. Turn the ignition switch to the ON position. 8. Turn the ignition switch to the OFF position. 9. Release the power unlock button on the door panel. The vehicle will lock and unlock the doors automatically. 10. Hold down the LOCK and UNLOCK buttons on the transmitter simultaneously until the door locks and unlocks. This step may take up to 30 seconds. 11. Repeatstep 10NOWfor each additional transmitter (including any existing transmitters). 12. Turn the ignition switch to the ON position in order to exit the transmitter programming mode.