Headlight and gauge illumination failed simultaneously

I was hoping you would see this as I know you have expertise in electrical stuff. I have the wiring diagram which I have enhanced to better show the colors. Part of my problem is that I get lost in the diagram! (I would upload my enhanced version if I could figure out how!) Also, I note that this diagram is for UK models. I'm not sure that matters but I'm left being not sure. A question about the diagram - I see a wire on it that (e.g.) is yellow with green dots. Am I guessing correctly that this represents a yellow wire with a green stripe? Plus, and I may be off track on this but, I don't see how the dimmer switch would affect the gauge illumination. According to this diagram, there is a gray wire with a black stripe (?) that goes from the dimmer to a lighting switch on the right handlebar. This switch is not on my bike (the ignition switch turns the lights on and off in the US) so this would be different in the UK. I am not sure how to test the switch without dismantling it from the handlebar.

I have the multimeter. I know how to use the voltage and resistance features on it but the rest of it just scares me.

@mike3 my reference to the dimmer switch is to the dimming of the high beams to your normal headlight. Both your headlight and your hi beam indicator would be affected by that. I am going to change the schematic and will post the one from the Yamaha workshop manual supplement. It is only black and White but it does display the issues you mentioned in regards to the switch etc. The diagram is for the 1100S/SC but those are identical. You should have power on the Blue/Black cable on your headlight as well as on the Red/Yellow past the headlight fuse. Just measure it if you do not mind. Check for actual power on the fuse.

Thanks, I have the B & W one in the Clymer manual for this bike. I would expect that the high beam indicator not to light if the headlight circuit was interrupted (I could be wrong). What stumps me is the gauge illumination lamps are out also. There are only five fuses on the bike - the main fuse under the seat and four spade type fuses under the indicator light panel. If the main fuse was blown, the bike would be completely dead so I know that fuse is good. There are two 15A and two 10A fuses under the indicator light panel. As far as I can tell visually and with the multimeter, they are good. The Clymer manual doesn't specify which fuse protects which circuit but they all look good to me. I would guess that if the headlight is protected by a fuse (probably), it is one of the 15A's. I'm going out and poke around in there some more; maybe I can figure out how to test that dimmer switch, and I will try to run the checks you suggest although on the headlight plug I'm seeing GR, Y, and BLK

which agrees with the schematic. Thanks for the help!