Tail light failed on the Nerrandera trip. No alarm on the instrument panel. Checked the lamp, didn't work when 12V was applied. Bought replacement lamp. No joy. Removed lamp, measured open circuit volts at the lamp holder. 5½V. Perused Bert's diagram of the bulb monitoring unit. The first item after the light switch is what? Fuse?. Anyway, my understanding is that when the light is switched on, the current drawn by the tail light operates a reed relay which switches an earth to the transistor doo-dad in the dotted box. Being chronically technophobic these days, I don't really understand what happens inside the dotted box.

Any suggestions as to where the other 7 Volts are being lost?

It is quite easy to remove and bypass the bulb monitor relay, I have removed mine. You can then eliminate if that is causing the problem. The removal instructions are on the web somewhere.

not all of them are reed relays ulrick ....

i have a couple here with resistance wire ( voltage drop principle )

we have seen a few posts that suggest that the pc board solder has broken from vibration etc on the pins that connect to the loom in the bmu ( bulb monitor unit )


we have also seen seats and shock absorbers pinch the cables before it gets to the rear globe ...in some cases shortng out and blowing fuses

but also check the connector that sits in the rear cowl that goes from the wiring loom to the globe holders ...it is a spade type multi pin connection ...(undoable connector ) they corrode up

you can see it plainly with the rear lamp remooved from the bike (sits vertically )

get out the deoxit again ?

does the warning light work as normal on startup ....then extinguish with the brakes activation ?

just had another thought

if you turn the key switch on to the park position ...what is the voltage then ?

if it is right it could point to some corrosion in the right hand switch or a connector under the tank ....so no volts is getting to the bmu for it to work properly ?

If all else fails, train a mouse to sit in the brake light with a box of matches. Attach the 5 volts you have to the mouse. Good luck.