Instrument cluster - "idiot" fuel light not working '85 K100RS

[Red]

I need to get my fuel light to come on when I start running out of gas! Everything in my instrument cluster works with exception of the fuel light. My bike does not have a fuel guage. I'm interested in pursuing fixing the fuel light because I ran out of gas yesterday and the fuel light did not come on ...  >:(

I just pulled off my gas cap and with a flashlight I could see that I have a gas fuel sending unit in the tank that looks like a "stick" standing up right. Checked with BMW and their microfiche shows this unit is different looking, has a swing arm attached to post.  ??? This is causing me some anxiety and confusion. I am confident that I can mechanically get to these existing parts and pull apart, test, etc.  Anybody have any information on the stick type sending unit and the swing arm type sending unit?

It might be that I have simply have a burned out light bulb for the fuel light ... any advise on the approach to and taking apart the instrument cluster, to check for burned out bulb, for a '85 K100RS?

[mystic red]

Yea, I might check that bulb first. There should be 4 recessed nuts on the underside of the cluster. Don't know how you get to them on k100RS but I had to remove the windshield assembly on my LT to access them. If you can get a socket on them (try a 10mm) you've got it made. Remove those, the giant plug, and you should be able to put it on your bench face down. Then just take out the screws in back. Might want to do all the bulbs if it's a pain in the ass to access so you don't have to do it again for 50K. Duck had an LED upgrade at one time but he's on the road back to his pond right now. If he stops somewhere with internet access he might chip in with more advice.
It's really not that big of deal to do. Like almost everything else on this bike it's doable but a little tedious
Do you have a Clymers for your bike?

[Red]

Oh, I know ... I don't have a manual yet. My debate has been a Haynes or Clymers or both! If you say so I'll go with the Clymers ... thanks. I've sort of looked at my cluster and I'm thinking that it would be a simple approach to get the cluster off and access into it. But, my luck, what looks simple turns into a nightmare ... so I ask all that I think have experience. If I have to get into my tank I want to have some idea at what I am looking at and how to deal with the fuel sending unit. It bothers me that the BMW dealer can have the fiche for the '83-'85 K but cannot identify the sending unit that exist in my tank. ???? I am going to further investigate ... Thanks for the response.

[mystic red]

Duck will be able to help more on the sending unit. He's had a few of them and parted more out. Check out that bulb first. Replace with OEM. They're pretty tough. Now if that doesn't fix it THAT could be a connection, either broken or dirty. I've heard of wires breaking in the tank but clean up the connector that plugs into the tank. Good luck.

[frankenduck]

If your bike is an 85 then it should have TWO fuel idiot lights. An amber indicator marked 7L that comes on first and then a second red indicator marked 4L that comes on next when you only have about a gallon left.  If you only have one idiot light then somebody put a later instrument cluster on which is not designed to work with an 85 fuel level sender.

[Red]

Ahhhhh ... I see ... at the bottom left corner there are two light windows on my cluster. You have just explained to me what both those two light windows represent. I had figured that one of those windows is for the fuel but still I still needed to figure out what the other window was for. Thanks so much. I'll move forward now and I think I will start with the the two fuel light bulbs in the cluster and if I don't get satisfaction there then I will pull the tank off and start investigating in that area. I have to pull the tank anyway to work on my front brake switch cable that has a short somewhere ... thanks all.

[mystic red]

Hey Bill, I think you'll find the wires coming out of the tank and the connector (at least on an LT) is connected under the right side panel. But like I said before, no experience with an 85RS. ;) If you haven't pulled the tank yet, it's high time you do. ;D

[frankenduck]

Mystic Red: The 85 tanks are completely different in terms of the fuel level sender which enters the tank in the front left corner of the tank and is a completely different beast.

Red: Does the bottom of your speedo face plate have an amber and red lens - marked 7L and 4L respectively?

[mystic red]

Mystic Rod: The 85 tanks are completely different in terms of the fuel level sender which enters the tank in the front left corner of the tank and is a completely different beast.

Red: Does the bottom of your speedo face plate have an amber and red lens - marked 7L and 4L respectively?

Dammit, I had a disclaimer, no experience with K100's and if you pull that rod ch1t again, I'm comin' strong.

[Red]

Sorry, screwing up on the post...errors... there are two light windows at the bottom of the speed plate. Both windows are red in color and there are no 7L or 4L anywhere to be seen that I can see.

[Red]

I went to BMW dealer this morning and got printouts of the microfiche for the '85 tank, sending unit, and instrument cluster. Also picked up an original (ordered previously) user manual for the '85 K. With interest, the manual shows a picture of the fuel light with only one arrow pointing to the window on the right. It says the light will come on when the gas in the tank hits a level of 1.2 gallons. Nowhere does the manual show what the window on the left is for.   ????

[Red]

Picture of RED's '85 instrument cluster on the bike

[frankenduck]

I went to BMW dealer this morning and got printouts of the microfiche for the '85 tank, sending unit, and instrument cluster. Also picked up an original (ordered previously) user manual for the '85 K. With interest, the manual shows a picture of the fuel light with only one arrow pointing to the window on the right. It says the light will come on when the gas in the tank hits a level of 1.2 gallons. Nowhere does the manual show what the window on the left is for.   ????

You got a later rider's manual.  There's two idiot lights in an 85 cluster.

[Belplasca]

You got a later rider's manual.  There's two idiot lights in an 85 cluster.

Actually, there are two idiot light windows on the later clusters - but the left hand one is not normally connected...

(Some riders use it to indicate when the fan is running, but that's non-standard...)

So, if you have two windows, but they are not marked with the capacities, you probably have a later cluster... Not sure what you're going to have to do to get the light(s) working, but checking the 25year old bulb(s) will be a good start!

Bob

[frankenduck]

There were two idiot lights connected only on 85 and earlier clusters.  You can also tell an 85 and earlier cluster because the lenses are yellow (right side) and red (left side) marked 4L and 7L respectively. 

On 86+ bikes both lenses are red and the right one was never connected until it was used later as an ABS warning light.