Year and more info might help. Anytime you have something modified a lot, more info is better since we cant make certain assumptions that we might normally make.
Switch and sense is the wire that goes from just off the solenoid wiring to the gauge IIRC. IF that circuit is not seeing 12 volts, nothing happens. If you read any of the good online write-ups, pay attention to the part of the write up that mentions not disco'ing the stock power cable at the solenoid - it mentions why (about the s&s wiring).
Once again, we dont really know how your wiring is modified exactly.
The conventional power ground is not a pin upgrade or connection. It is a motor to chassis ground.