cruiser477

I need some help. Restoring a '70 Fastback and having issues with the fuel sending unit. I have grounded the lead from the dash and received the pulsing light with the test light. So, the wiring and CVR are working properly. I also get the same pulsing on the test light with the temp and oil sending unit leads. Now, I have used the pick end of the test light placing it into the connector boot that plugs into the fuel sending unit. Then, using the alligator clip and putting it on the threaded nipple on the sending unit, I get no pulsing. Ground issue right? However, with the pick end still in the boot ( wire lead ) I put the alligator clip to the body of the sending unit where the fuel line connects and now get the pulse. Why in the world would I show good ground on the body of the sending unit and not on the threaded nipple of the sending unit where the lead plugs in? By the way, it's a new sending unit and tank. I did have it in and out several times when trying to get it to work and stop leaking. A new one has been ordered as well. Maybe I got a junk one out of the box.