Tail light is not a light

The tail light on my 1986 VFR750 has just stopped working. It is not the bulb, but something upstream of that. I am not sure where even to start. Are there likely and accessible intermediate points that I can get a meter on?

 

Here's a link to the wiring diagram if you need it

http://vfr.bikersoracle.com/index.php?threads/1986-700-750-wiring-diagram-large-pics.120472/

 

Start off checking the fuses.
I'm presuming the front lights work when the switch is on.

Lift seat and locate tail lights follow cable back to multi connector . Either using a test bulb or multi meter. Earth one side and touch other to the relative wire to see if you get a reading. Colours vary but could be green/ yellow. Ignition and lights must be on.

 

Run a new wire and leave the (apparently) broken one alone.
Possibly the easiest way, if also the cheesiest.

 

having this same problem myself

first thing to try is to reach under the fusebox to find the main plug b etween the wiring harness and the ignition switch, and clean the contacts within the plug.