Both FB water gauges DOA in dash rewire

[Genevatexan]

My big flybridge dash rewire project had a casualty: neither water temp gauge will operate and that kills both at the lower helm as well. There were a few wires difficult to label and photograph and it turns out it affects water temp. The sender wires are bright yellow and there is no other at the helm, and the port shorter than starboard so they are correctly connected. The power for the three wire gauge (power, sender, ground) is a full 13 volts and was pulled from ignition on switch, but the grounds have gotten a little mixed up. Question: Does the sender in the engine have two wires and require both all the way to flybridge. I am getting multiple different readings in the gauge depending on the ground selected, since I have a few grounds confused. Since the senders are correct and the power correct, my assumption is ground is wrong. Does the ground for each engine need to remain distinct with these two gauges?
I have been trouble shooting this for 3 weeks and cannot get to the bottom-neither the old gauges or the new will operate.
As an aside, the new Stewart Warner gauges are poorly crafted- I went against advice of this forum and bought because I wanted dead matches and no issues with lower helm and senders, but the gauges are really poor quality. Ammeter with no ground to make bulb work, uses same two terminals for hot wires as for mounting by insulating bracket, temp gauge was a 240, they no longer have a 230, crummy housings, old bulb design, it goes on...
Should have listened and ordered from the FLA vender recommended.
Help on trouble shooting water temp gauges greatly appreciated....
After that, photos of finished project to come. Very happy with the new gauge mounting board though...Kent

 

[Nonchalant1]

Are they original AC type gauges? If so, are they reading full hot or full cold? These are "fail safe" type gauges that will read full hot if there is power but no signal from the sender. They will read full cold or random needle, wherevfer it happens to be if there is no power to the gauge.

Doug