Simplex NAC circuit on 2001 in trouble

Fact 2001 2001 8021 Repack 2001 8023 Expanded Repack 2001 2075 Class A Signal Module 556 257 2001 2076 Dual Class B Signal Module 556 874 NAC circuit on 2001 in trouble Adding additional Horn Strobes There is no compatibility issue Check for a reversed A V unit or misplaced jumper causing an open Lift off field wiring and temporarily install proper EOL resistor typically a 15K in place to see if trouble