No spark on 340

73 Duster with 340. Last month put in new resistor, ECU, Dizzy cap and wires. Started and ran fine, tried to start today and no spark to plugs. Test light grounded to body shows bright on positive side of coil in all key positions, but from positive batt to positive coil as a jumper test light goes out in key start position. Everything else seems ok, any ideas. I have a buyer and this is frustrating.