When I turn The key in the ignition the car seems to hiccup real bad before it turns on ( sounds like it’s not going to turn on at all) but it’s not making a clicking sound like a bad starter, then when the engine does crank the dials in the speedometer shake really fast for a solid 5-10 seconds. Plus when driving sometimes the Bluetooth goes in and out now and it started when the engine was having an issue cranking. the battery is good and alternator is good, no check engine lights either. But when I go To lock the car with the key the horn sounds really weak and puny now. I thought at first maybe bad gas but I did A gas treatment and ran out the old gas and put new gas in and it’s still having this problem. Also tried a fuel injection cleaner and got no different results. A bad fuse? A bad starter relay? Maybe it is the starter? Electrical issue? It has still started every time I’ve tried but it sounds like it’s BARLEY doing it. It’s been going on for about 2 days now.

2013 Mustang gt premium / auto trans

 

Not sure what it could be but sure seems like an electrical system issue, not fuel.

 

Bad grounds on chassis, bad terminals at battery, bad connector(s) somewhere, bad/chafed/shorted wiring (mouse issues?), SJB, BEC... just a few things to check on, but yeah. This might take an expert if you're not in the field of automotive electrical wiring chasing, 'cause that's quite a list you got going weird on your car...

 

yep, sounds like an electrical issue, not enough voltage or intermittent voltage

how do you know the battery and alternator are good? how old is the battery?

 

First thing I thought, sounds like a failing battery.