Temp gauge not working

[70CHEVYBB]

I am trying to get my 72 in order. I have a problem with my temp gauge. PO had put in after market gauges and tied up extra wires. I found the temp gauge wire and touched it to ground and the gauge flickered. I figured it would work. I installed a sending unit and it all the way past hot. I then found out the sender was light only. I then installed one for a gauge. After warming it up it goes to the low side of the red hot mark. I do not think its the gauge because I switched out the gauge cluster from my 70 that was working. Could I have a ground issue? I did use teflon tape to seal the threads.

Thanks, Wes