The condenser is a radio noise filter, as the IVR or regulator is INSIDE the gas gauge on a Rally dash. It goes on the +12 stud
If you have not, I would eliminate the gauge wire as a possibility. Supply 12V power to the proper cluster pin, and ground, and ground the sender wire. Get the wire codes from the manual, follow them to the cluster connector, and follow the board traces to the gauge pins. Not that hard. One is 12V IN to the IVR, one pin is 5V OUT of the gauge which jumpers to the other gauges to supply them, and the 3rd is the sender