I have two water lines running to the house. With one connected everything is fine but if I disconnect that one and use the other I have low pressure in the house. Two facts: the water pressure of the new line outside is greater than the water pressure than the first line. The reason I am switching if the water pressures varies on the first one pretty often during the day but the new line has even pressure although greater. Why would I have less pressure in the lines in the house when I connect the new line>

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Why would I have less pressure in the lines in the house when I connect the new line>

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If the old line was galvanized then It's most likely clogged with iron oxide,(rust).
You ask the question.

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What happens if water pressure too high entering house

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If your house pressure is above 80 PSI it will put a strain on elbos and faucets/valves. It will also cause your shower head to leak when you're filling the tub. What's your house pressure? Back to you, Tom