The ground comes from the transmission. It should ground the solenoid in 3rd and 4th gear. Not just 4th. If its not grounding check the switch at the trans with an ohm meter. The system is designed to give vaccum advance in 3rd and 4th gear only. dont take this the wrong way but unless you are going for a 100 point resto you are wasting your time. The car will run better if you go right to either ported or manifold vacuum. Your car will have better acceleration and fuel economy.
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