If the battery terminals are tight and clean and the battery is charged, we need to see if the starter is getting power or not. If no power, we have a wiring/power issue, if it is getting power and not working, the starter is likely bad.
First, I attached the wiring schematic below for the charging system. If you look at pic 1, I highlighted two things. First, the park/neutral switch. As a test, see if the vehicle starts in neutral. If it doesn't, go to the under-hood fuse box. In pic 1, I highlighted the ignition fusible link. Pic 3 shows the location of the link in the fuse box. I need you to check if it's good. In addition, confirm there is power to and from it. Here is a link you may find helpful:
https://www.2carpros.com/articles/how-to-check-a-car-fuse
If you have power and it's good, then we need to check the starter relay. I highlighted it in pic 3 also. If there is another relay with the same part number, switch them to see if it makes a difference. If there isn't, here is a link explaining how to test a relay:
https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit
If the relay checks good and all power supplies are good, then locate the starter solenoid. See pic 4. On the starter, there will be a heavy gauge red wire. It is straight from the battery and has 12v at all times. Additionally, there will be a black wire with a yellow tracer which is a smaller wire. That is the trigger wire. It should only have 12v when the key is in the start position. Have a helper turn the key to the start position while you check that wire for power. If there is power, the starter is likely bad.
Let me know what you find or if you have questions.
Take care,
Joe
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Friday, December 31st, 2021 AT 7:41 PM