What does the yellow wire do? '84 VF500F

[Tyy]

I have undertook the task of rebuilding and modifying an '84 VF500F. I have a wiring question. What does the yellow wire that connects to the instrument cluster do?. I have figured out every other wire on the bike, I am adding an LCD display, HiD Headlight Assembly, and LED blinkers all around. Every wire is labeled and ready for soldering. Except the yellow wire. According to the diagram it connects to one of the ignition coils and one of the spark units. On the other side of the wire though, it disappears off the diagram past a pin connector. Following the wire myself I can see it go into the body of the gauge cluster, but I wont know what it connects to until I take it apart.

 

If anybody has a clue what it is supposed to connect to, please let me know. One sneaky suspicion that may be of use, is the fact that the bike wont start with it unplugged ( I think [many things and do-dads were unplugged] ).

 

This is a link to the diagram http://imgur.com/0zhzloN

 

I think something suspicious is afoot, maybe we should [redacted] into this more. [redacted] are keeping something from us. 

[Captain 80s]

Let me take a look on one of my bikes and diagrams. 

[Tyy]

I've had an idea. After looking over the wiring diagram, I think there is a typo/error in the colour labeling. Coming from the tachometer is a wire labeled as L/G for "Blue/Green". I thought it was just a coincidence that it was near the end of the yellow wire on the pin connector, but I think it is an error. The signal from the temp sensor and the tachometer should not be interchangeable should it? Yet from what I see it appears that way. It would also make sense if it were a typo because the yellow wire comes from the spark plugs where the tach signal should come from.

 

I'd appreciate any second opinions on this. This diagram is from a genuine '80s Honda manual after all.

[Guest]

I think it's the L/G tachometer. The tachometer takes positive, negative and signal taken from ignition coil (Y)