Look to the back of the alternator. You will probably find the small red wire broken or disconected. Very common failure. While you're down there, check the black oil pressure sender wire and the large red battery wire on the back of the alternator. The wiring wraps around under the crank. The large red terminates at the junction block by the headlight relay. The small red and black go into the engine harness and terminate at a rectangular 8 pin conector about the middle of the firewall.