OK - this item is on the firewall of my 73 240z, on the passenger side near the battery. As you can see it is looking every bit of its 39 years. My question - what is it and what does it do?

Thanks for any help you can provide!

According to the BE section of the FSM, that is the Throttle Opener Relay. The coil looks to be energized at startup. It activates a solenoid. You can find a diagram with the solenoid on page EF-10 in the FSM. If the carbs have been swapped out, I would guess that the solenoid may be long gone.

I've seen it on several 240z and wondered what it was myself. With that are you saying that it was only on the 73-74 Z's firewall? I've got a 05/72 and though the jackass who owned the car before me removed half the original items from under the hood have spent 6-1/2 years bringing it back to its former glory. I do not think my z had one but could you confirm this?

There is no mention of the relay or solenoid in the BE or EF sections of the 72 FSM.

Thanks, Steve. My '73 received a triple Weber set-up sometime in its past so the next question is, does the relay even do anything anymore. I don't think I want to get rid of it but I definitely need to do something to clean it up. Right now it looks like it came off the set of an Indiana Jones movie.

No, the relay doesn't do anything anymore. I didn't dig into the EF section to see function of the servo that the solenoid actuated, but I can say with a high degree of confidence that the triple Webers don't need that functionality.