sending unit issue

[MrLimo]

Hey all, thanks for reading. I'm new to this forum, and new to the world of the 60-66 GMC/Chevy (Notice the GMC first?) world! Purchased one recently and it's gonna be a slow build, but I'll start a thread with some photos so you all can see.

I have an initial question for everyone tho, as it has me a bit stumped regarding the fuel system.

66 GMC truck (I believe it's a C1000) has the original gas tank, sending unit and gauge. When I bought The beast, gas gauge did not work. Figured I'd buy a new gauge and sending unit to replace what was factory. After investigating, realized the fuel line comes out of the mount for the sending unit, so I decided to see if I could fix what was there. Pulled the sending unit from the tank & saw that the flat "wire" that connects to the outside of the sending unit was broken. Soldered a new one on the end of the flat 'wire' that's factory, and attached it to a new screw sticking out of the top of the unit and it works! Great, can see how much gas I have so I don't run out (had already done it twice at that point!), but come to find out it actually works intermittently. No rhyme or reason as to why, just sometimes it registers the amount of gas, and other times it's pegged at Full.

Any suggestions?

Thanks!
Chris