Help identifying this

Jimmy1971 said

Doing some wiring clean and and looking for some help to identify an electrical component on the firewall, passenger side corner. I cannot find it in the service manual wiring diagram. It has a blue wire that runs back to the ballast for a 3rd blue wire. Not sure what it is for. Any help would be appreciated. 1971 Plymouth Scamp with AC if that helps.

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As surmised, the device shown in the pictures is part of the NOx (oxides of nitrogen) system for California cars in 1971. It is part of the overall Cleaner Air System (CAS).

The device in this case is for an automatic transmission car, and is the control unit part of the system. The thermal part of it senses temperature in the cowl plenum. The control unit triggers the solenoid vacuum valve based on temperature and vehicle speed.

The following image shows the system layout:


The following image shows the wiring diagram for the system:


For more information, see section 9A of the 1971 factory service manual.