2003 gmc envoy xl electrical issues

That tends to point to an issue with the BCM and its data network. You need an auto electrician with a pro grade scan tool computer to diagnose the issue as it is a strange one.

test battery and alternator and the connections/wiring -[new doesnt mean free from defects ]

Bad plug or broken wire at the plug, at the alternator. Pull the plug off the alternator. Turn the key on and check for power and ground at the leads. No reading, probe the wires a couple inches back. If a read there fix or replace the plug. If you have a 3 wire plug, best to use an ohm meter. Test each wire separately. At the pin and a couple inches back on the wire. This test may include testing the wire back to the PCM and fuse panel. You'll need wiring schematics for this. The PCM is what fields the alternator to charge and supply power when the engine is running.

Could be the neutral safety switch if it won't crank in neutral or park, could also be the starter has failed.

Sounds like a flat battery. Just enough to power your lights but not enough to power the starter motor. Try recharging the battery.and check battery connections are good.

Who did the testing & did both the
battery & alternator fail at one time?

Auto Zone has a repair facility & did the work?

What codes are present?

Did anyone look at a data base, to see what
the message your getting was & the solution?

Hello,
I suggest checking your starter motor. If the starter motor is staying engaged it could be a bad solenoid or a bad ignition switch.

I hope this helps.

Roy

This is probably due to a faulty alternator, or bad battery.

Attach the car battery to a second car, using jumper leads. If the accessories work fine in this situation, then you probably need to replace your alternator.

have the car scanned for trouble codes and get back to me with the codes. most major parts stores will do this for little or no charge,get back to me with the codes

youmay have a dead cell in your battery mine acted like yours igot it running at home i tested the battery and found it only had 10.6 volts this indicates a bad cell tip: if your battery is 4 or 5years old replace it because it needs it also you can damage your alternator by waiting till the last crank