Chasing fuel gauge and tach issues...

[speedo]

71 2.2 w/ CDI
Tried two different fuel gauges, and completely disassembled and cleaned the sender (which was really gunked up). Replaced the sender in tank and still no gauge. Checked the 3 pin fitting on top of sender...all looks good. With gauge out of car, put voltage to it and needle jumps???

Tach bounces a bit hen ignition is keyed, then nothing. Replaced it with a different tach, same thing. Tach has three terminals on back...+,- and trigger. I jumpered the purple black trigger off the side of the dizzy thinking I might have a bad wire in the harness...nothing. I did a continuity test to the black purple wire and it is fine. Took the tach around to the back of the car while it was running. Pulled power off a fuse, and ground from the chassis, and then jumpered the purple black wire from the dizzy...nothing. This isn't supposed to be that hard. The dizzy on a 71 uses the purple black wire to send a signal to the CDI, right? And that same signal goes through the 14 pin plug...through the body up to the tach. What am I missing here? is there a way to test the tach other than putting it into another car? Someone mentioned that I need to make sure I have a CDI tach. Wouldn't any tach 70 and later be CDI a CDI tach?

TIA for your help guys. I can live (for a while) without an operational tach...the fuel gauge is a bit different.

Speedo