When I first got my r65 the indicators would only work when the hazard flasher switch was engaged. And even then somewhat erratically at best. Nothing worked if the hazard switch was in the off position. After much befuddled frustration and with the help of the forum and snowbums website I finally tracked it down to a pesky worn out diode.
A diode is like a one way gate for electricity. electricity can flow in one direction but prevents currents coming from the other side. When they break, electricity can flow in both directions, therefore into circuits which shouldn't have power and causing all sorts of random and seemingly unrelated behaviours.
I found a wiring diagram
http://www.bmwmoa.org/forum/showthread.php?t=39617 for an '85 K100 has diodes. I'm guessing that the K75 would be in the same boat. The diode looks like
. This pic (courtesy of cartft.com) shows the real diode at the top and the symbol to look for in wiring diagrams at the bottom.
I'd begin with finding and testing all the diodes on your bike.
You'll need a multimeter. If you don't have one they cost about $20-30 for a reasonable digital multimeter with a diode test function. To test, simply select diode mode (or the ohm) check with the polarity in both directions. current should only flow in one direction - so if it flows in both directions - the diode definitely need replacing.
The other thing to check with the multimeter is the core function of the switch and the wiring to and from the both sides of indicator circuit, as well as the hazard switch.
