The issue is the radiator fans do not run (federal 94 S4 with A/C) either at temperature (>92) or when the A/C is turned on (this may be misleading as its possible there is no R12 so the low-pressure switch may be stopping it from energizing?) Regardless they should work at temperature, so:Checked all fuses and relay bases for heat damage/loose connections-all good Tried swapping relays, no difference.Removed the AC request relay (I'm not sure if running in diagnostic mode energizes this one) The rear AC relay is in.Jumped pins A-B on the ALDL connector, fans do not run with ignition off or on (also tried with AC request relay on and off) They should run in diag mode, but they don’t. Decided to take the sensor and ECM out of the equation first. Jumped Pins 30 to 87 on the front relay, fans run! This indicates an issue with the rear relay. Removed the rear relay and jumped pin 30 to 87, fans DID NOT run (checked for +12V at pin 30 - ignition on, +12v confirmed) Double checked fuse 13 and it was good. I then checked for continuity from pin 85 on the front relay to pin 87 on the back relay (pin 85 on the front relay gets its ‘fans on’ signal from pin 87 on the back relay) and did NOT get continuity (yellow line on attached pic). So, my question is what is there between pin 85 on the front relay to pin 87 on the back relay that is suspect? The wiring diagram shows two items, an RHC 12 ?? and an CBHC 2 ?? anyone know what these are? On the A/C circuit there appears to be a Zener diode but that should not stop it from running in temp mode. I then ran +12v to the front relay (pin 85 with the relay installed) and it energized the relay and operated the fans, the perplexing issue though is that the fans do not run in either temp or A/C mode for the rear relays, but do run when jumpering 30 and 87 on the front relay. Anyone come across this gremlin?