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Re: Stockish Looking relay ???
Quote:
Originally Posted by ray_mcavoy
According to the factory repair manual, that is the "speed switch" for the TRC (Throttle Return Control) system. The TRC is supposed to open the throttle a little bit while the truck is coasting in order to reduce hydrocarbon emissions.
That "speed switch" gets it's RPM reference from a connection to the HEI TACH terminal. It's contacts are supposed to close above 1900 RPM and send power to a vacuum solenoid. That in turn switches vacuum on/off to the throttle lever actuator mounted to the carburetor.
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I Could see this but its tied into the oil pressure system not the tach. 
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