Yes its a relay but its normal. There is a charge light
in the volt gauge. Has it been on while the car was running recently? It would signal an electrical problem
or lack of a charge. The default for the system unfortunately is to not allow operation if a problem exists, so in essence the car is not starting for its own good.
Things to check: all fuses, fusible links, battery/starter
cables etc. If you can jump the car off, try the old trick of disconnecting the battery to see if the alternator and/or battery is good.
The 75 280z has a seat belt interlock that causes the same symptoms if it's wasted (like mine). I was unable to find the fault so I shorted the appropriate pins on the starter relay (on right side in engine compartment in front of battery under black box) and it works fine now. I'm not sure what year they started or stopped putting the seat belt interlock in the Z.
If you replace the relay and still not getting spark, you may need to replaced your ignition Control Module (transistor control module) under the passenger side dash. This is an expensive part, so call All Z East to get an price estimate from the salvage yard. Good luck.