Hello,

I am currently building a k100 and installed the bep 3.0, a new tachometer and the munit.
As I want to keep the Feature of not starting the bike if either a gear is already in place or the clutch hasn't been pulled, I also added a relay to make it work with the output from the BEP.

While the clutch variant works without issues, I have a weird issue with my gear indicator. Both neutral as well as 1. gear are shown as neutral in the tachometer and therefore also allow the start of the engine. Beginning with 2. Gear, the light is off.

I have scimmed through the forum already and there are a few reasons, why it might be an issue.

Bad wiring, bad connection or issues with the BEP 3.0
last but not least an issue with the sensor in the gearbox.

As I have not found anything with this specific issue, I simply wanted to ask what you think is the most likely issue in this case.

Kind regards from Germany


TheplayVik

Oh yeah, it is the early k100 rs(pre 1985)

The gear position sensor can fail, this would give the strange results you are experiencing. Try disconnecting the sensor and testing its output as you change through the gears. The three coloured wires each connect to the ground wire (brown) in a different sequence for each gear position. If this thread is still unresolved tomorrow, I will dig out my notes showing which sequence relates to which gear. The sensor can be taken apart and rebuilt with care.

There are four wires from the sender. One is brown and is for connection to ground, the other three are signal wires and they are switched to the brown wire in various sequences according to whichever gear is selected.
The three signal wires are:
Yellow/blue stripe
Yellow/black stripe
Yellow/white stripe

They are switched to the brown wire as follows:

First Gear: Yellow/Black, Yellow/White
Neutral: All three
Second gear: Yellow/Blue, Yellow/White
Third gear: Yellow/White
Fourth gear: Yellow/Blue, Yellow/Black
Fifth gear: Yellow/Black

To test the switch, disconnect the four way connector on the black cable that comes out of the gearbox under the battery tray. Identify the different coloured wires and check for continuity between the Yellow/whatever wires and the brown wire as you select different gears.

Okay, thank you for the update on the wire selection depending on what gear is in place. From what I am seeing, my main focus should be the yellow/blue wire since that is the one not usually in use during gear one, but neutral it is

If you have an early K100 the gear position switch is way past it's "best by" date and probably needs to be removed from the transmission and have it's internals cleaned and the potting replaced.