Those resistance values suggest the sender is working. But there do seem to be different ranges used by different senders and gauges, see this thread, which also suggests how to work around that. Some presumably common sender ranges are in the calibration table in this Stack manual. is there any documentation for your new gauge? While you've got in bits take the opportunity to test the whole lot on the bench without any of the possibly problematic wiring, either feed or earth. Fused 12V supply. Completely new wiring from that through the sender to each gauge in turn, slowly moving the float from end to end. How does each gauge respond, and is the response consistent?Jonathan PS: ... so what do we think the conclusion here is, that the wiring is good, my Caterham gauge is faulty and my Racetech gauge needs a special sender? Possibly, but you may be able work with that sender and some trickery.