Hi. I have a 86 non turbo 300Z. The main fuel gauge is inop, but the secondary one works fine. I replaced the sender assembly with a new Nissan unit, and that did not fix it. Also got a new working gauge, and that did not fix it either. Have power to the sending unit, and the gauge. I don't know what the voltage should be to the gauge, or sending unit. Secondary fuel gauge works fine. The gauge I used as a replacement was a tested, and functioning gauge. Ground problem? When I turn on the key, the main gauge moves directly towards empty. It does not move up towards full when power is off, just maybe an 1/8 of an inch, and then when power is supplied it moves down that little bit to bottom out. Any help, or suggestions would be greatly appreciated. Thank you.

 

Just off the top of my head, sounds like a wiring/connector issue. The replacement OEM sending unit should have reported to the gauge correctly. But your problem continued. This tells me the problem may not have been your old sending unit but was between it and the dash gauge. The gauge sounds like it's trying to work backwards now - which also says bad wiring.

I wish there were a short cut to this but there isn't. The only solution is to trace the wiring from sending unit to the gauge. Since the gauge makes two separate reports, there have to be at least two feeds from the sender - plus a ground or two.

Your FSM has big electrical diagrams. (XenonZ31 Reference) They are too hard to work with unless you take them to a print shop and get prints at 11 x 17 - Find the sending unit and the gauge - and trace the feeds end to end, through the connectors between them. Locate the connectors in the circuit. Trace the feeds on the diagrams with colored markers from end to end, get out your circuit tester and go for it. At some point, you will find a dirty/corroded connector, a broken feed or a reversed hot/ground connection. Separate, clean and reconnect connector. Check readout on gauge. Works. Then congratulate yourself for doing a hard job right.