Took out old battery, put new one in and now the car won't start. It has power, lights, radio but no horn?
My car has 60000 miles.
My car has an automatic transmission.
When I have had this occur, either there is a smaller wire that wasn’t reconnected, or the security system became enabled at some point. It is possible to short out computer modules, but you would have seen a large spark at some point during the battery replacement. I suspect it is security oriented.
Remove the negative battery cable, turn the ignition key into the run position and reconnect the negative battery cable. This is one method of resetting the security system. Another is to put the key into an external lock cylinder and lock and unlock it two or three times in a row. Usually this works on the drivers door, but it may need to be done on the passenger door.
If none of this works, then you have a genuine problem that is a coincidence at the time of replacing your battery. What I am not sure of is if you have a no crank condition or do you have a crank no start condition. These are two very different situations.
If you’re unable to address the issue yourself, I recommend you have your starting issue diagnosed by one of our qualified technicians in person.
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