Check the fuse, and if the fuse is good. Then check the fuse terminal with the ignition keys in the on position. The ignition lock may have gone bad and will need to be replaced or the wire harness from the ignition keys down the steering column has gone bad. The ignition switch it self may be going bad and may need to be replaced.
If you have many keys on your key chain, this will promote the ignition keys to fail. The ignition switch's job became more complex as accessories like radios, electric windshield wipers and heater blower motors were added to vehicles. Moving beyond its original role as a simple on-off switch for the engine's ignition system, the ignition switch was also designed to supply electricity through an accessory position on the switch. This allowed accessories to function in a key-on, engine-off situation without overheating and oxidizing the contact points in the engine's distributor. As more accessories like power windows, power door locks, power seats, air conditioning and electronic automatic transmissions were added, the ignition switch's job became even more demanding.
Today, the ignition switch is a complex device that powers numerous electrical and electronic systems throughout the vehicle. In fact, the newest version of the conventional ignition key is an electronic device that identifies the driver and allows him to activate the starting system on demand.
Most ignition switches incorporate spring-loaded, sliding contacts to transmit adequate amperage to individual fuse and relay circuits. As these contacts begin to wear, they may lose their ability to make perfect mechanical contact. In other instances, they may begin to oxidize due to heavy amperage flow. In either case, the contacts begin to develop electrical resistance that reduces amperage flow through the ignition switch.
Very few ignition switches fail catastrophically. Most begin to fail intermittently and are usually sensitive to temperature and humidity. If the internal sliding contacts are heavily greased during assembly, the grease may begin to harden and inhibit mechanical contact during cold weather. If the switch fails during heavy accessory loads, the internal sliding contacts may have become heavily oxidized or succumbed to heat distortion and loss of mechanical integrity. In any case, most ignition switches give ample warning of an impending failure via intermittent ignition or accessory operation under various conditions of temperature and electrical load.
Good luck and hope this will lead you to addressed the issues your having with your Jimmy. Keep me posted, be glad to know you got your car running 100% again soon.