Cadillac Repair Questions? Ask a Mechanic for Answers ASAP
When you try to start it, do you hear a single click with each time you turn the key or a series of rapid clicking?
This does sound like a weak battery. Sometimes the battery can have enough voltage to get some things working, but the starter itself uses amperage to crank. I suggest you start with a jump start. Leave the donor vehicle attached for about 15 minutes, then try to start your truck. If it start or even cranks, you know you are dealing with a battery issue, and you should have it tested.
A poor ground could also be the problem. So check the negative battery cable where it connects to the body and the engine. Make sure it's clean and tight and not swollen.
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