Apart from bad connections, those two gauges share the distinction of being fed by the voltage reg chip on the foil. You surely understand that for the resistive type gauges to work consistently they need to be fed by constant voltage . The chip puts out around 10.5 

Alistair 

> On Sep 13, 2017, at 2:14 PM, Don Hanson <dhanson928@GMAIL.COM> wrote:
> 
> Yesterday I had a period where the fuel gauge and the coolant gauge both
> were reading very low, and inaccurately... I think this may be a ground
> issue.
>  In the past, my temperature read lower than it was when tbe connection
> was loose at tbe sender, but baving two instruments in tbs same gauge
> reading too low, that is Odd...any ideas?
>   For what it's worth, wben .my coolant temperature gauge showed "cold" I
> bad a fright... thinking I could have no coolant...(I gave up on my
> "coolant level" Warning light years ago).   but a check of the other gauges
> (no alternator light) normal oil temp, normal Oil pressure..that easily
> confirmed the temperature was ok...And I use my trip meter for my main fuel
> quantity calculations... I'd driven 260 miles only since my last
> gas...there we're at least 5 gallons of gas in the tank, yet the gauge
> needle was below the red...
> thanks, Don Hanson