No, you do not need a connector bar for a semi-automatic only M14-type rifle. The military M14 rifle was originally designed as a select-fire (full- and semi-automatic) rifle.
Military M14s are usually issued as semi-automatics only (the same as the L1A1/C1A1 rifles).
The M14 operating rod has a notch on the bottom of the operating rod hump for the connector bar. The connector bar attaches along the right side of the rifle by the operating rod operating guide slot. The connector bar attaches to a hook on the connector, that is held in place by the selector shaft, shaft lock, and pin. The connector, selector shaft, shaft lock, and pin attach to a lug cast into the bottom of the right rear of the receiver.
When the selector shaft shaft lock is replaced by the selector lever and spring, this allows the connector to function to connect it with the lug of the automatic sear that is attached to the trigger.
When the selector is locked in place by the shaft lock, the connector cannot contact the automatic sear and full-automatic fire is prevented. When the selector lever and spring is installed and the lever set to full auto, the rifle will fire automatically as long as it has ammunition and the trigger is pulled. Closing of the operating rod and bolt trips the auto sear through the connector bar and connector pivoting about the selector shaft.
Unnecessary parts for a semi-auto M14-rifle:
1. Connector bar.
2. Connector.
3. Selector shaft.
4. Selector lever.
5. Selector lever spring.
6. Selector lever pin.
If you really want to make certain, replace the M14 trigger assembly with that of an M1 Garand. The Garand sear does not have the trip lug of the M14 sear.
Master Gunner