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Generally GM makes the spade terminals in a way that the connector can only go on one way IF it needs to go on a specific way. You might notice an area in the black connector where GM cut out some of the black plastic and that is were the raised tang in the terminal will go. They made it idiot proof.
Yes the male connectors are keyed, so you can only install them on the gauges one way. The female ends have slots to accommodate the keys. This ensures that you can not plug a connector into the wrong gauge, or plug the connector on in reverse. The pictures below are from a 1973 center cluster, so there is no oil pressure connector, which is another connector yours will also have. (In 1973, oil pressure was connected by a capillary tube from the block to the gauge measuring "real" pressure, not electrical conversion via a sending unit as occurred starting in 1974.) Here are the following pictures to illustrate:
And as you can see...you can not mess up how the connectors go on the terminals due to how they are made. Each gauge is different...an thus the black connector ends are made to match each gauge specifically.
A case in point where it does not matter is the dark blue and yellow bullet terminal ends that go into the windshield washer pump. It does not matter which one goes in where due to the connector ends are the same.
75 Center Console Gauges
