tail light electrical issues -- blowing fuses etc

[therm]

Hi all,

I have been working on my 1985 k100 and almost have her back on the road -- today when rewiring the rear tail light i got no brake light.

i have cleaned the ignition and my left control switch,  cleaned and retighten the ground under the tank.

it worked yesterday.

today when testing with multimeter i would get 11.9 to tailight but only 3.9 when brake was applied.

i kept blowing the top fuse several times and on my last attempt the bulb monitoring device started smoking.


any tips or advice on what to look for???

i am decent with bike repairs but electrical is my least skilled.


thanks

[therm]

any thoughts??

[motodude]

It sounds like you have a short somewhere.  And, you need a new BMU cuz you let the magic smoke out.

You'll have to trace the short, but I would start where you last worked.  I'm not dissing your work, but if it worked yesterday and it blows fuses today, it is a good guess that whatever changed between then and now is probably to blame.

Tom

[Zipster]

Yep sounds like a short somewhere. A rubbed or nipped wire close to where you were last working.

[WayneDW]

When that happened to me I found out eventually that the rear tire was rubbing on the wires running to the rear light.

[therm]

aha !!

turns out the rear brake switch wire was pinched when i put footpegs back on after messing with the brakes.

of course i figured it our after testing every other idea literally twice and reopening ignition switch to make sure i didn't somehow get it back together wrong.

sunny and 80 degrees here tomorrow and i have a day off from work --  going to take her for a spin!!

[JamesBearPig]

Thank god for you guys. I did the same thing and pinched the rear brake switch wires. 10min search on here and she’s back.