My 2007 GMC Sierra 1500 is baffling mechanics & electricians for over a month! The seat belt light will flash while driving & other dash lights as well. Or, the power door locks will start freaking out (up/down/up/down) & the RPM & Speedometer gauges will act like windshield wipers. Once either scenario happens, I know that the very next time I turn the truck OFF, then EVERYTHING will be dead. No lights, no sound, nothing. Occasionally, the CD player will be loading & unloading, but that is the ONLY thing that will be "working". Let it sit for a minute & it all comes back (but the clock, etc has been reset). One shop replaced the ECM (did not help), another placed 5 or 6 new grounds under hood. 175 amp fuse was replaced. For now, I am just driving it like nothing's wrong, since it will start for me until the next time it freaks out. But it will always start again. Battery & Alternator are under 1 year old. Can anyone help? It's a nightmare for me & the technicians!
Is there an after market alarm system or radio or other electronic component installed in the truck?
If there is then you would want to check the wiring to any or all of the devices for proper power feeds and grounds. If someone who installs these types of electronic devices and doesn't really know what they are doing they can mistakenly tap into a computer power feed wire or computer ground.
When the truck has its moment; have your mechanic check the wires on the ignition switch. Pay attention to the power outputs of the ignition switch. With a test light check the power wires on the output side of the switch while the problem is happening. If the problem is occurring and the switch is the problem then the test light will flash just like the lights on the dash.
Check out these suggestions and get back to me with the results. We can go on from there.