Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
03 Jeep Grand Cherokee. Stared having problems starting. Parked it one day wouldn't start the next. Replaced the alternator, starter- used parts starter came from running car. Battery now drains unknown to me why. I think needs new battery as well when fixed. Have found Scannerdanner on YouTube. Watched 3 videos on no crank no start. Would like help of diagnosing the actual problem instead of guessing from others and replacing. From the Pittsburgh surrounding area.
Let's get you cranking, again. Then, we'll work on the battey draw.
Check fuse 14, and fuse 8, in the engine compartment fuse box. They should have power all the time. Check fuse 31 in the under-dash fuse box. It should have power while the key is in the CRANK/START position. If both of those check out, we'll move on to the Starter Relay.
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
Fuse 14 good fuse 8 good fuse 31 not broken. Didnt test in crank position got to replace terminals for battery. Negative battery terminal is broken and not good connection.