It just quit running
 

Suspect an electrical problem. Running down the freeway ~75mph and it was like I switched off the ignition key. Still had battery power, RPM went to zero, Check Eng & Batt light came on, radio still playing Kicks. Coasted over to the shoulder. No oil underneath and it turns over fine but doesn't kick off. Fuel pump still primes. Replaced EEC Power and Fuel Pump Relay. Started momentarily, but cut off again. Tach doesn't move when cranking. Poked a spark plug into one of the leads--no spark. What next?

'91 Explorer, 4WD, +340K miles
 

Might need to know yr, model...

check for corrosion on all wires into battery cables, inside rubber as well

check the connection at the crank sensor, none/bad, no spark

I see from your profile it's a 91, and I'd guess it's a 4.0L pushrod engine with the DIS ignition. With the CEL light on, the ECA should have set a code, and that would be a good place to start. Last week I just read about the tach and ignition, but can't for the life of me remember what it said, and I can't find the info again. I believe you should have a tach signal during cranking, and that's your best clue for troubleshooting this. If you find the cause of the no-tach problem, I believe you'll have fixed your problem. Hope this little bit helps...

Pull codes to see if anything comes up. Primary suspects would be the ignition module (located in front of the battery), coil pack, or a broken wire.