It ok to use regular gas on a 2005 infiniti q56 if not what can happen?

Well that does not make much sense. Your seats have power but nothing else. Have you check your main fuses. If it has no power your seats would not work. Might also check your battery wires for corrosion or broken battery connections

Can you conect the ground wire with any part on the body

The transmission has failed is what is most likely wrong.

fuel gauge troubleshooting.

yes....87 is perfectly fine and should be used all of the time with confidence. The higher octane fuels can sometimes help with a knocking engine but are mostly used for higher end vehicles.

you need a new radiator this happened with my sisters nissan

Where is the fuel gauge fuse on an 06 Infiniti G35

Are you putting regular gas in it? Sometimes a knock can happen when you don't use the correct gas. G35 are high performance and need 87-91 octane gas

Same thing happened to my 2003 Infiniti G35 Sedan. My mechanic has adjusted my brake booster (above the brake pedal) and so far it has been ok.

It means the computer has detected a malfunction in one or more of the numerous systems it monitors. There's no way to tell which code it has set without scanning it. Did you happen to get gas right before the light went on? The light will go on for something as simple as a loose gas cap. Check to make sure the gas cap is there and is tightened properly. If that is the problem the light should go off in a few drives.