Pulsating Voltage in Gauge Wires??

Trying to get the original temp and oil pressure gauges to work, I found a new problem.

The voltage in the gauge-wires are pulsating from 0 to 7 volts, this happens with the engine turned off as well.

Is this normal?

(If I short the gauge-wires to ground, the gauges goes to max, so they gauges are working.)