I will be in the process of changing my 83 K100 instruments with some from a later K75 (thanks Rick). A few questions if I may
Are the "guts" of both interchangable? Can I use the old casing with the new instruments?
The circuit controlling the two low fuel lights died slowly over the last few years, so I can not place it in the new instruments and I am used to having no lights. Will there be a problem with the circuit controlling the one warning light or do I just remove the bulb ?

Your original was presumably an 83 so would have 7 screws holding the case together and that one from the K75 has 9.
It isn't difficult to disassemble, there are the 9 external screws to part the cases and 6 more inside then the innards lifts out.
There are 2 at the extremities about midway and 4 close together at the top centre, 2 are obvious and the other 2 are 10mm further out and a bit deeper, you may need to lift the plastic flexible circuit away a tad.

From what I can see of the circuits the only difference is the wire missing at pin 8 of the newer gauges which is for one of the fuel level lights. It should, "plug and play".

Thanks Rick.

Well I found out a few interesting things this weekend. Yes the new instruments will go into the old style case but the old ones will not go into the new case. It would probably work if a few holes were cut in circuit boards or things were moved about. The extra screws needed to put the back on cause the problem. It isnt an issue for me but I just wanted to put thins together so that I could store it safely.
The new gasket/o ring cost $1 at the local bearing place...if it had a bmw part number it would have been a fortune.

ainsjac wrote:The new gasket/o ring cost $1 at the local bearing place...if it had a bmw part number it would have been a fortune.

I didnt think of that. I need to go to the bearing shop more often.

Oh well, the BMW was $7 i think. I was surprised at how reasonable it was.

Hello to all,
Having trouble with my bmw fuel gauge (K100LT-1987) (it didnt work at all) and finding that it has serious problem, propebly the coil of the instrument was out of order, i found that in the market i can buy a VDO gauge that is exactly the same with the BMW and you can put it in the same case. Its connectors are exactly the same with the original (+, -, S=sensor). It costs 45 Euros , new, when the BMW (and propebly made from the same factory- VDO) cost the double.
It has also a small difference with the fitting screws, but this difference is so small that you can fit in the same case without trouble.
But when i connect it with the ocnnector, i found, that it works with the opposit (!) direction of the original! When the tank is full the needle is on the left side of the gauge (empty) and when it is empty the neddle was to the right side of the gauge (full)!.
I tried to change the connectors from + to - but the result was the same.
Finally i found the solution!
I put the sensor out of the tank and found that i can not change the polarity of the moving part of it.
Each sensor has a moving part wich is "running"  on a resistance coil , so that the instrument can "read" the resistance betwin the earth and the moving part.
So i have to put out of the chassis of the sensor the small plate that has the resistance coil and change the side, on it the moving part of the connector is "running".
Changing that, i have 2 results. 1. The VDO instrument is working properly (full-right, empty-left) and 2. I prolong the life of the sensor , because the most of the cases of sensor-troubles cause to the warn resistance coil because of the movement of the moving part! Changing the side where the moving part is running, you have a new sensor and also i new gauge with the half of the price of the original.
I hope that this information will be very usefull to you.

gntsakon wrote:
So i have to put out of the chassis of the sensor the small plate that has the resistance coil and change the side, on it the moving part of the connector is "running".

Did you disassemble the sender case, remove the fibreboard with the resistance coil from its mount,  flip it over and reinstall it?  If so, that is an interesting fix for many people who customize their bikes and replace the BMW instrument cluster.  Doing this modification makes the sender very much like Japanese type senders, resulting in more compatibility with aftermarket instrument clusters.

robmack wrote:

gntsakon wrote:
So i have to put out of the chassis of the sensor the small plate that has the resistance coil and change the side, on it the moving part of the connector is "running".

Did you disassemble the sender case, remove the fibreboard with the resistance coil from its mount,  flip it over and reinstall it?  If so, that is an interesting fix for many people who customize their bikes and replace the BMW instrument cluster.  Doing this modification makes the sender very much like Japanese type senders, resulting in more compatibility with aftermarket instrument clusters.

Yes, i did so as you exactly discribe.And all this because there is not easy to find the vdo instrument writing "BMW" in the second hand market and as new is more expensive. Also is hard to find senders in good working order and when you find them, they have a worn resistanse that means that they have sorter woking life . With this method somebody can have the sender as new with less money.

gntsakon wrote:And all this because there is not easy to find the vdo instrument writing "BMW" in the second hand market and as new is more expensive.

All the instruments for the old K's I've seen is made by Motometer, not VDO.

As I discovered (to my cost, when I ran out of petrol on the motorway) that my fuel warning light isn't working, rather than try to fix it, I thought about buying one of the round analogue gauges which fit into the plastic bit of the fairing where I think the speakers go on some bikes. 

I saw one for sale on eBay and almost bought it. The thing which made me hesitate was that there seemed to be only a very short lead coming from the back of the unit which had a plug on the end. I read somewhere that this type of instrument plugs straight into the socket from the sender unit. My question is, will the lead from the sender unit to the instrument cluster, be long enough to reach inside and around the fairing to meet up with the short lead from the new unit or is there a jumper lead which can be had to do that job?

No, it is not long enough.  BMW has an adapter cable that comes with the "Other Instruments" option and connects to a plug on the harness under the tank on the right side.  The adapter cable is part #19 in this diagram.


The adapter cable splits into two parts, one for the fuel gauge and one for the coolant temperature.  The under tank connector looks like a PC hard disk drive connector (white AMP connector).  This cable can be easily constructed using off-the-shelf electronic components.

 BMW has an adapter cable that comes with the "Other Instruments" option and connects to a plug on the harness


Thanks for this valuable information robmack I'll see if I can order that first.


Wish I knew how to get the title of each post into the entry box at the start of a reply, mine is always empty and I can never remember what the OP title was so have to keep scrolling up to look - and quoting a post includes this yellow background but I can't see how to get rid of it.

Aha, it went plain all by itself.

alibear57 wrote: BMW has an adapter cable that comes with the "Other Instruments" option and connects to a plug on the harness

Thanks for this valuable information robmack I'll see if I can order that first.

Check the bike carefully first, LT models did have these instruments as standard.
It's a yellow and a green connector.