Temp gauge issue

Flashing and ultimate voltage will depend on the load going through it. 
Unless one of us has upgraded with an electronic regulator then it will read a constant voltage with no flashing.. regardless of load. The gauges will be SLOW to read upward if that's the case but they will get there.

I always do the easiest first, working from the point furthest out until I locate the fault.

That's why I ground the lead at the sender to see what happens. it's simple, fast, and will tell a lot. If the gauge goes up, you know the gauge and wire are ok. Basic troubleshooting - do what will test the most components to start with, then based on what does or does not happen, branch from there.

If the fuel gauge works and is reasonably accurate - right there you have said a lot about that current limiter/regulator. You have shown that it is working at least in basic form or the fuel gauge would not work.

So if the fuel gauge is ok, or even reads but is off a little, but the temp gauge doesn't move - there's really no need to blame the regulator because the temp gauge doesn't move at all.
If the regulator was so bad that the temp gauge never moved, the fuel gauge would not function or would read WAAAAAY off.
So if the fuel gauge works, the instrument panel regulator is basically working. 
For me the next test is the next most simple - ground the wire to the temp sender.
if the gauge still doesn't move, you have shown a wiring, connection or gauge issue.
If it DOES move, you have proven a sender issue - and proven the regulator works.
Simple first. And all you need is a piece of wire.