J and L Nast

I have 2 Nissan Pulsars (1987 & 1988) NX's both had issues with Fuel Sending units Now I've got new Fuel Sending Units and all Gauges worked.. then they stopped working, then they started working again???? No idea? By All I mean Temp Gauges, Fuel Level, etc. Any ideas on where to start Trounbleshooting? I've checked fuse's sending units and temp sending unit. The odd part is is works, then next time I start it doesn't?

We got ours from TheRackDoctor he's Myrtle Beach area. I traded my old ones in for a core. I think the Website is https://rackdoctor.net/

How is the Body/Model/Styles code for each years of Pulsars? Like N12 etc...