A few years ago I decided to turn my 1989 K75S to the naked version. I bought all the necessary BMW parts, including the round headlight, the instrument cluster, the RT type bars and the radiator cover. During that modification, I used screws in order to screw the instruments to  the cluster, that were longer than the original ones. As a result one of the screws touched the electronic panel at the back of the instruments and caused damage to the copper circuit that controls the low fuel warning light. As a result the low fuel gauge doesn't work anymore and I always run the risk of running out of fuel without knowing it. I am guessing that it wouldn't be too difficult to fix the circuit by a specialist. However I do consider the idea of getting a spare, used instrument unit, (including both the tacho and speedo). My question is which K model instrument unit is compatible with mine, (all the 2V including both K100 and K75, or just the K75)? Are there any differences between early and later years?

Stavros
K75S 1989, 196.000km

From about 5/85 thru 7/93 the instrument cluster is the same between K75 & K100 with slight variations if ABS, and of course, mph rather than kph. The part number for your complete cluster is 62 11 1 459 917, 62 11 1 459 541 or 62 11 2 305 251, assuming Euro model, no ABS (too early) and kph. No explanation is given in ETK for the difference between the three units other than the typical BMW supersession of part numbers. Some of the earlier units had a moisture damping blanket fitted. The main plug for the wiring loom to cluster is the same throughout the year range specified. Earlier models (pre 5/85) and later models (post 7/93) will not correctly align, electrically. A lot of the guts of the clusters are fully compatible and you can peruse the part numbers yourself using an online ETK (catalogue) like www.realoem.com/bmw or others offered up by larger BMW dealerships.

Yassou

need to check the connector pins on the instrument unit

earlier models had flat pins

later models had round pins

your 89 needs a BEP 3.0