Starter motor won't crank...solved, with some advice offered.

[stuo]

I had a very interesting problem on a recently purchased 2011 DT 300i with 3400miles on it. It was starting and running fine...until it wouldn't crank. The lights and fuel pump were working but it failed to crank with either left or right brake lever pulled in. After comprehensive diagnosing done by Mike the Master, AKA "mjr" on our forum, it was discovered that both brake switches were not working. Both!

Because I always used the right brake lever to start it I didn't realize the the left side brake switch had previously burned out, then when the right side switch burned out neither side would work. If I had checked to see if the brake light was working the problem could have been avoided because the brake switch sends current to both the brake light and the starter relay, so if the brake light isn't lighting the starter relay isn't working, either.

Mike carefully took the switches apart and found burned contacts, which he burnished with a red Scotch pad, lubed them with dielectric grease, snapped them back together and Walla! Good like new! (Amazon sells generics that fit: $7.99 for both switches, postage paid!) How long the restored switches will work is the new question.

Why did both switches burn out after only 3400 miles? Has anyone else had this problem? Obviously there is too much current for the switch contacts; either the switch contacts are too flimsy or the brake filament is drawing too much current. One solution: replace the incandescent brake bulb with an LED to reduce the current drawn.

Has anyone done an LED replacement? Any comments or suggestions?

[ole two wheels]

Haven't done an LED replacement, but my left brake light switch bit the dust with a tad over 3.000 miles. Seems to be a weak spot for the DT's. Several other folks on here have replaced BLW's on theor DT's.

[Stig / Major Tom]

Well, the good news is that failed switch is easily diagnosed and cheap to fix.
Saves tearing into the whole electrical system.
Best to check 'em both from time to time is my take-away here.
Stig

[mousejunks]

According to the service manual, the starter switch and brake light switch are wired in series to the start solenoid and brake light. The fuse for this circuit is 15A. It is possible that the brake light switch (a type of microswitch) is not rated for this amount of current.

[ole two wheels]

You could just be unto something mousejunks.. HD had a bunch of bikes with very low miles, needing ignition switches replaced. Turns out that was what the problem was. The contacts were just to light and could't handle the heat. (That was about 20 years ago.) All to many times The Motor Company has allow the customers to do their R&D for them.

[mousejunks]

It's probably bad design, my old Aprillia Sportcity burnt out its ignition switch at 12,000km.

[de dee]

 I changed the front turn lights at low milage at 86,000 Km.  still no problems, 

[stuo]

Follow up: I replaced the stock brake bulb with an "extra bright" LED that draws 1/5 the current of the incandescent bulb, so that should eliminate the brake switches from burning contacts.

If you replace your bulb don't use the $1 LED's you see on ebay: the brake light is barely brighter then the running light. The bulb I used comes in a two-pack at O'reilly and cost $25.