Fuel Guage Goes Up Then Partly Fades -- 72 Swinger

Finally got some time to get some incremental information on this. I built 3 resistors (10, 20, and 70) and verified them with a digital meter. Results:

10 ohms -- the needle went up to 3/4 and promptly settled back down to 1/2. It proceeded to wander a bit around 1/2 +/-.

20 ohms -- the needle went up to just above 1/2 then settled back down to about 1/4 with some tight wandering afterward.

70 ohms -- the needle went just above empty and settled just below empty.

So it's clearly not just my janky spectra sender that is causing this problem. This does eliminate the sender ground as a problem since the resistors went straight to battery ground and I'm still getting this behavior. My best guess at this point is that my $15.99 IVR from Classic Industries is a dud. (I assumed the one sold by CI was solid state due to their statement "replaces the original mechanical regulator with modern electronics" - and maybe it really is, but the evidence at this stage is pointing its finger at that regulator being bad.)

Since this is a daily driver and I don't get much time to pull the dash repeatedly, on my next dash-pull I'm going to replace the IVR with an RT-Engineering solid state. I've already cleaned and verified all of the dash connections and verified conductivity for the full length of the fuel sender wire. I know I have the skills to build a robust IVR from scratch, but I just don't have the time to mess with it.

The temp gauge is not working, but I've found that problem is break in the wire somewhere between the temp sender and the gauge. I'll probably just run a new wire from the temp sender to the instrument panel, rather than trying to trace the problem with the old temp sensor wiring. Then I'll test the new RT regulator. If I'm still having the problem, then I'll know it's gauge failure and I'll try new gauges.

And some day I'll be able to see how much gas I have and what temp my engine is running.