Last week, my 1974 BMW R90/6 developed a new electrical malady – in the ignition switch.
This switch has four positions: off, park, run, run+lights. It would start and run just fine, but when I switched from 'run' to 'run+lights' (required in TX), everything would die. No lights, no ignition, no horn – nothing, zip, nada.
I opened up the headlamp shell and tried some tests. Tried high-beam only – same failure. Tried low-beam only – same failure. Unplugged the headlamp assembly – same failure. Hmmm.
Time to look at the switch:
I think this switch is unique to early /6 models – so what you see here may be different than on later /6 years (YMMV). I took this image to document the wiring. I could have seen the problem if I had looked closely. Look at the areas near “A” and “B”. No gap at all between the metal case and the insulator at “A” - but look closely at “B”. See the gap? (Note: the images expand if you click on them).
I disconnected the battery. This is not my first rodeo.
To remove the ignition switch, you must remove the outer nut and spacers then remove the 13mm bolt (with its spacers) on the opposite side of the headlamp assembly. Then you can gently tilt and drop it down slightly. Removing the ignition switch is then straightforward.
When I had the switch in my hand, I noticed that the insulator was being forced outward by the internal springs and was not flush with the metal case. I told myself to fix that when I put the switch back together – not knowing that I was looking at the root cause of the problem.
I very cautiously took the switch apart – being very, very careful to look for small springs and contacts that might try to escape to the workshop floor. Note the missing metal at the 2 o'clock position on the metal case.
I took the switch contacts and the associated three tiny springs out and and cleaned everything with alcohol. I could see no electrical problem or broken bits.
This switch has a series of four detents and a ball bearing/spring mechanism to locate the rotor in one of four positions. You can just barely see the detents near the 5 o'clock position on the right, above. As I was cleaning (and re-lubing) that part of the switch, I noticed that the ball wanted badly to escape its channel – making the switch miss the 'run+lights' position. Aha! The missing peened section was allowing the ball to leave its channel just enough for the switch to over-rotate, bypassing the 'run+lights' electrical connection.
I completed cleaning and lubing the switch and put it back together – held in place with a temporary clamp. I re-peened the two good sections and then did my very best to re-peen the area with the missing metal. Here are side-by-side images, the restored peen and the problem area:
Looking at the very end, it should be easy to pick out the two normal peens and the repaired area (near the “K” mark).
Note: 30 refers to both terminals near the center (+12V), terminal 58 (park/running lights) is at the top, 15 (ignition) at the left and terminal 56 (headlamp) is at the bottom.
Fixed – at least for now. The ideal repair would be a new switch, but as of this writing, they seem to be NLA and difficult to find used. If I have to go back into the switch, I think I will use a drill press to make a couple of very tiny radial holes through the metal case into the insulator near the failed area and tap in some tiny pins. That might be the best I can do until a switch turns up.
Other ideas?
cln – Nick
WB5BKL
