so you could have pinched the line so even if it looks good it could be broken internally.
you can ground the line in the engine compartment and then turn the key on and see if the gauge moves.
then if it doesn't try grouding from the bulkhead connector and test again.
IF it doesn't work from the bulkhead and you are sure you grounded it, then maybe the gauge died.
if it is possible you pinched the line grounding out the line causing the gauge to peg and you didn't notice, you might have burned it out.
This is the proper way to troubleshoot the gauges. All I can add is that I too have had trouble with Teflon tape but not with thread compound. An easy check is to measure the resistance from the sender body to the pump housing. Should be zero.
