1978 R100/7 Wiring Question

[Deleted User 62]

Trying to get a friends 1978 R100/7 back on the road. We have the coils wired correctly; black wire from points to right coil and green one to left coil. There is an extra black wire coming out of the harness near the left coil that doesn't show up on the wiring diagram. It's not there on my '74 R90/6. Any ideas as to its function? Tach is mechanical.

[Kurt in S.A.]

'78 should be electronic tach...is something non-stock on this bike? This is a reasonable wiring diagram for the '78s:

http://www.omnilex.com/public/bmw78/78r100wire.jpg

There should be a small jumper wire between the two coils. The '77s were wired to be ready for the electronic tach (tachs were mechanical) and there would be a wire near the coil that goes to the tach (not shown on the above diagram but it is in the BMW manual). Could be the wire you're talking about. Certainly the /6 would not have that wire.

Kurt in S.A.

[Deleted User 62]

Got it, thanks! While it doesn't show up on that wiring diagram, I checked the '79 one and found the extra black wire to the tach.