The orig. sending units (& gauges?) tend to read high eventually. NOS replacement brought the needle back to center.  More reasonably priced units may turn up eventually. Just check ePay regularly.

6 VOLTS/POS. GRD. NW INDIANA

There is only One sending Unit used for 56 Cars and Trucks for a Gauge only. No Lights were ever used for Temperature.B6C-10884 or B6C-10884-A are same application. Finding an original is hard and right now the only one on Ebay is not in my price range.

  

I have a mechanical Temp gauge in the front of Manifold next to thermostat housing. it works fine. the original dash gauge has always worked fine until i took engine apart last fall. now The Sending Unit that was working fine quit. Bought a Dennis Carpenter replacement  which seems to be the only one available no matter where You buy it. Not working consistently

  

My experience has been that the gauge & sending unit should be a matched set. 

When I converted my dad's (now mine) 55 Tbird to 12v, I retained the original gauges and sending units. Although I question the accuracy of the original gauges, I saw no appreciable difference in their accuracy once I converted to 12v. I have since bought Autometer electric temperature, oil pressure, and voltage gauges and sending units, but the original gauges will be retained as well. 

When I sent my B intake manifold to Ted Eaton for porting, he also drilled and tapped it, just to the right of the thermostat cavity, for a temperature sensor, having said that the location provides a more accurate reading that the location at the rear of the driver's-side head. I later drilled & tapped my Mummert intake in the same location for the Autometer sending unit.  

I bought one a couple of years ago and had the same issue. No reading and then suddenly it would come good. I think the issue is that it is a B6C 10884 without the A on the end. I suspect that it is fine for a light but no good for a gauge. They do come up NOS on Ebay occassionally. I bought one to replace that unit and also bought a spare about a week ago. There's one there now but it's very expensive.

I bought a Repro Temp sending Unit From Dennis Carpenter. B6C-10884-A. Not keeping constant setting. Has anyone else had a problem with One of His senders? I would have preferred NOS but impossible to find. Thanks!