Quote:
Originally Posted by Pepi
Not on the 73 1/2's, they use the 4th gear to energize the solenoid to allow vacuum in 4th gear.
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Not 100% sure about 73's but all earlier systems worked so the solenoid was turned OFF by the switch in the trans when you put the trans in 4th gear. That way, the solenoid was off under highway (4th gear ) driving. I can't amagine they changed the system just for 73.
If for what ever reason the solenoid is turned off, vacuum passes through to the vac advance in the distributor. If you unplug the switch at the trans, disconnect the solenoid, remove the fuse, etc, it will advance the timing.