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Turned off the truck one day. Got up the next morning and went to start it and when i turned the key everything,all the gages all the lights everything went dead. Like the pcm b fuse was blowen but it wasn't and it isn't. Changed the starter and the fuel pump to no avail. When i hook up my OBDII scaner during a jump start it wouldn't communicate with the truck. My next idea is to change the alternator

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    Why would the alternator fix this? Is the engine a 6L? Make sure the engine has a ground. The two grounds on the rear of each head tend to go bad. Check them. When the one on the driver side goes it can cause similar symptoms. – Ben Sep 26 '18 at 1:27
  • Yes, there are three different engines listed for the '05 3/4T Silverado. Agree with @Ben ... there's no reason to change out the alternator, as it would have no effect as to whether it would start or not. If the battery is good, you need to check the wiring and all connections. Start at the battery and clean all of your connections from there back. Also, look for any bulges in the heavy gauge wires running from the battery. This would be a sign the cables are bad. – Pᴀᴜʟsᴛᴇʀ2 Sep 26 '18 at 1:32
  • Did you check you battery? Broken batteries can have an internal short when under load that would look about as you described. – Daniel Sep 26 '18 at 8:36
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Don't swap out any parts, you have an electrical issue that needs to be resolved. Replacing things isn't going to make any difference unless you know what needs to be swapped and will waste your time and money. Either your battery is bad or there's a problem with the electrical connections in your car's electrical system. It could be a simple fix that costs you nothing.

First check your battery terminals and connections. Corrosion or a loose connection can cause this exact type of problem. Remove the connections from the battery posts, clean them free of dirt and corrosion, then put them back on and tighten.

Next, check your battery voltage with a multimeter. It should be at least 12.2 volts, which is enough to start your car. Below that it won't crank but you'll get lights. If the charge is very low either your battery has quit, you have a battery drain which is sucking its charge when the car's not running or the alternator is not charging the battery. Leaving a map light on overnight can drain your battery, it could be as simple as jumping it and you're good to go if that was the case. If you jump it and it runs check the voltage while it's running, you should see at least 13 volts. If not then you may have a bad alternator or voltage regulator.

If your battery voltage is good and the battery connections are good then it's harder to troubleshoot, there will be a problem with the wiring or connections keeping the power supply from flowing. You need to work your way up the system and figure out where that is. I would start at the fuse box, pull a fuse out and use my multimeter to read the voltage between the hot side of the plug and the car body. If there's no voltage then you have a problem between the battery and the fuse box, if there is then you most likely have a grounding issue.

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