If this is for your 85's, the cars that have tachs use a different pick up point.

However, if you use an 83 or earlier tach, the set up you refer to will work.

How many prongs on the back of the tach? One with two prongs is what you need for the early tach wiring.

I would think you can get the sensor from Fastlane.

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83 SD

84 CD