New Standard T-Series ignition module.  This sits inside the distributor.  This is a stock replacement module, for non-computer controlled HEI distributors with the 4-pin module.   Fits the following:

75-79 Firebird/Trans Am w/ 301/400/455 Pontiac, 403 Olds, 305 Chevrolet Engines, V6 Engine
75-79 Camaro w/ 305/350 Chevrolet engines, V6 engine

NOTE : Please ensure you are ordering the correct part and diagnosing your problem correctly. Opened/installed electrics are not returnable.