Help... Adding a second temp gauge

I tried install a Bosch temperature gauge but the needle is bouncing continuously.

My goal was to splice off the factory temp gauge and add the second Bosch gauge where both of them would be operational.

Trying to diagnose I isolated the line to the power, sensor, and ground with no luck. I did this by using a long wire with roach clips on both sides. I first tried to go directly from the gauge to the sensor, then to the ground on the battery, then to the positive side on the battery, and I am still having the same issue.

Any thoughts?

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