[Nick_R_23]

I would pull your cluster and test the dark green wire with an ohmmeter, one test lead at the cluster connector, and the other at the sensor connector. If there is an issue with high resistance or no connection, then obviously correct it (firewall connection might be an issue), but if there is little to no resistance in that wire, then either your sensor is faulty, the gauge is faulty, or they are mismatched in resistance values. You mentioned earlier that your gauge pegs when the sensor wire is grounded, which indicates your gauge is working. At that point, I would suspect either a bad sensor, bad ground on the sensor (teflon tape can cause grouding issues. Use PTFE paste instead), or the sensor is functioning but has a different resistance range than the gauge and is not compatible with it.