something to check first, small black box in front of battery. If those are OK I'd then verify all is good with the battery wires including the one going into the fusible links box. Also check the ground lug that's right behind the battery's negative terminal - sometimes that frays over time (at the bend). Lastly if that's all good - perhaps a bad ignition switch? Last thing I'd check but something to consider if the car has a lot of miles...