My 2002 blazer keeps dying on me when I am driving, and sitting at a light. The speedometer goes down, the battery light comes on. my mechanic said its nothing mechanical. I took it to a shop that does electrical work and they said no codes are showing up, nor any history of issues. What else could it be?

Answer: Your mechanic needs a new career because it sounds like you have a bad alternator. It sounds like you need an alternator, turn the car on and check battery voltage, while the vehicle is on it should read around 14 volts running, if you read battery voltage which is around 12v your alternator is not producing necessary voltage to keep the engine running.

Low system voltage will cause the speedometer to go down and of course the battery light to come on. Not sure why the charging system was not tested by your mechanics.

Another possibility is a bad ignition switch. The ignition switch is what supplies voltage to most of the vehicle systems. One quick way to check on the Chevy Blazer is to have the truck running and tap on the head of the key with a small hammer or something similar. This will usually cause the switch to act up because of the shock of tapping on it. This is a common problem on the Blazer. The electrical contacts inside the ignition get corroded and cannot pass enough voltage through to the vehicles systems. They can very touchy and be fine one moment and cause problems the next.