Motorcycle Repair: Yamaha XS400 headlight, illumination lights, rd400

Question
Wow. Thanks Randy!  That saved me some work for nothing.  I found an old article somewhere that said the 79 RD400 had a headlight relay, so I kind of figured.  Now, what about the gauge lights?  Meaning, the illumination lights, not the "idiot" lights. Are they on the same circuit as the headlight? That would be wierd, to not have gauge lights unless the engine is running. They don't have power either, but I did check the bulbs and they are all good.-------------------------
Followup To
Question -
I have the engine out of my bike (79 xs400) and working on the lighting. I am building a streettracker) I have everything hooked up, (aside from engine breaker and alt. wires, obviously) The turn signals work (don't flash), horn works, etc.  Headlight is dead.  No juice to it.  Don't know if there is juice to the switch. Battery is a little low.  Should the headlight work in this state?  Is there a headlight relay that must be supplied a certain amount of juice for it to work? I read that these bikes had a relay that turned the headlight on when the bike was started, but once the key was turned off, the headlight would not come on until the bike was started again. If this is true, problem solved. I don't want to try and fix what isn't broken.


Answer -
Hi Mike, no motor no head light. The headlight is a rather large load which requires some amperage. It utilizes a relay which allows the light to be wired with heavily insulated wire whilste your switch gets much lighter insulated wire. The headlight relay powers up from a lighting coil in the engine not the battery. So the engine must be spinning to provide the power for your light. Good idea Yamaha came up with...nothing more frustrating then trying to start your motorcycle and the headlight is on as soon as the key is turned, seriously depleting precious battery power. Yamaha said " Hey, lets let them at least get the thing started before that headlamp comes on"  smart

      sincerely

         randy

Answer
Hi Mike, the clocks (gauges) should be illuminated when the key is switched to run. There are some exceptions though. Your bike may be an exception, due to its age. I really dont know for sure. If it has an oil indicator that should illuminate when the key is switched to run ( bulb test) and the nuetral indicator should light up. It may just be the back lights for the clocks dont illuminate until the Head light does. I would need to look at wiring diagram for your bike to be sure.. sorry

         sincerely
         randy