2002 f150 all warning lights are flashing and it wont start
Sounds like a bad battery. Try a new one or a different one if you have an extra battery around. If battery is new, have someone hold the key to the ON position like they are trying to start it. While they are doing that, get under the vehicle and rap on the starter with a hammer. If vehicle suddenly turns over, that means you need a new starter.
What do mean flashing? Do you mean they are on when the key is turned to the run position, which they should, or are they flashing abnormally?
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