That's the closest thng there is to a dignostic port on a '75 D-Jet. There is a Hall-effect sensor that is aimed at the harmonic balancer, looking for a nub that is aimed at the sensor when the engine is at TDC. The only use is for a timing meter. The little 'shoe' on the fender that looks like a wire connector is the terminal for an external tachometer for use while setting the idle RPM.

Mine was missing when I got the car, and it really isn't needed. If I could figure out how to get a 36-1 tooth wheel on the balancer, it would be perfect for the Megasquirt project to use the sensor bracket.

Scott

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