R100S electrical gremlin questions

My tach and speedo have never illuminated since I bought the bike. The bulbs and connectors were checked by Terry during his service of the unit.

I am getting about 10.5-11V at the ports when I check. The high beam indicator, the turn signals, neutral lights all work fine. The fuses in the bucket look good. I am trying to trace the gremlins. Not all of the connectors are hot with a meter, so I am wondering if any of you know which connector correspond with which functions? Is there a diagram available? The factory manual isn't muc help. The photo was the best one I could borrow from Google images, but notice that it's upside down. Any help is appreciated

IMO, the best wiring diagram is the one in your owners manual. It has what you are looking for.

Shoot it.

It's the only humane thing to do. :huh

But other than wise ass remarks I don't have any real help to offer.

I would start by making sure that your ground wire is well grounded/attached/cleaned etc... an awful lot of electrical gremlins can be traced to poor grounding contact. Brown wires are your grounds per euro wiring specs.

The backlighting is a grey wire, again per euro wiring specs. It should come "on" with the first click of the switch. You might also just go back and forth with the switch... on/off/on/off/on etc a bunch of times... mechanical switches can get dirty and, again, make poor contact.




I started a thread years ago about adapting an Acewell to the Slash 6... pretty sure it identified which pins do what, etc.... I'll see what I can dig up.



this might get you a start anyways....

See if the bulbs are burned out and if so, replace them. Look for the wedge base bulbs at an auto supply place before doing the BMW bend-over.

The bulbs can also rattle out of their holders. If you get some dim light, guess what?

Don't hesitate to open the pod. Be gentle with the gasket (good and cheap thing to replace.) Look for cracked screw bosses and repair if found. Keep track of which screws go where. If you need to patch the circuit board I have some pics somewhere of the procedure, but unlikely it's broken unless you get hamfisted taking a bulb out. Clean bulb connection with an electric eraser with the eraser sharpened to a point. Don't use ink erasers, only ones for lead pencil.

Now that I've read what I posted yesterday, I don't think my first post was clear. The pod has been completely serviced, right down to new bulbs by Wirespokes a few months ago. Everything inside the pod is fine. The inner row of lights inside the pod (green neutral, yellow turn signals, ect..) are good, as is the blue high beam indicator inside the tach. What I am getting is less than 12V at the plugs that go into the pod and I am trying to track down the voltage loss. While I think it might be a weak ground, what I would like to do is identify which of the silver pins in the back correspond to the bulb which they light. The manual I have (Clymer I believe) is useless. I know the brown wires are ground wires, what I would like to do is trace them to the mounting point and find out if they are corroded. Does anyone know where these ground wires terminate?

Do you know how to hack the instrument plug pinout? I have one here in a harness I'm tearing apart but I don't know if that pinout ever changed.

Anyway I can tell you how to do it but it might be a bit of telling and I don't want to bother if you know.

What's your voltage at the battery when you check the voltage at the pins?

Mine drops around .25 to .5 volts. You can also use an ohm meter to tell where the pins connect. If I read your post correctly, you think the guage lights aren't working due to the low voltage?

On mine, the speedo light seems to stop working every year. Mine has enough play in the housing that the bulb holder can twist and one of the arms comes off the circuit board. I've replaced the holder and the buld. You can probably make a small piece of metal to push between the bulb holder and the circuit board to increase the surface area of the connection.

Don't know how to hack and everything is still in the factory bundle so I really don't want to peel away the harness tape, but I suppose if you know the location of the ground pin, I could use a jumper to find the tach and speedo pins.

The ground for the instrument lighting is shared with the brake fluid level switch.

Bingo. Check the plug and find the pin socket that is common with the frame (clean metal on the frame). If the ground is poor you will have to check resistances rather than using the meter continuity function. lowest resistance will be the ground.

You can then check the instruments by applying 12 volts between the ground on the instrument plug and the various other pins. The tach will be the one that does little to nothing unless you click the power on and off fast. This gives you the pinout on the cluster and then go backwards and map that to the plug. From there use a wiring diagram to see which wire goes where and check connections.

The wiring diagram shows three different types of grounds. The frame grounds tend to be close to the device, the battery grounds are in the cables. The frame grounds are the most vulnerable followed by grounds passing through plugs. Some grounds pass through the connection board so you can break the circuit there and check resistances both ways.

On your big black plug, pinch female connectors #7 and #12 to slightly deform them out-of-round. Then reattach the plug and test.

Here's a better photo borrowed from another thread here. Which connectors are #7 and #12?

In general terms, lower left and upper right. The females are individually numbered on the black rubber plug. That's how you can correctly identify which male pins correspond to the numbered females.

What model year is your R100S....as the 12 pin plug lineup varies from year to year.

I might be able to get you a wiring diagram of the 12 pin plug and what pin wire goes where. Let us know model year. Thanks

Pull the back of the cluster off so the ribbon circuit is exposed. Put your ohm meter on a low setting and put one probe where the bulb connects with the circuit and one on the male post. Move from post to post until you find which one it is connected with. Right that down and put the probe on the other connector on the board and see which post it's connected to. Then get a battery and put 12v to those posts.

Sorry--1977. Must have forgot to include that in my original post.

Here's wiring diagram + legend for the numbered items for 1977 R100S . I have one and this I keep handy.

The 12 pin connector that plugs into the tach/speedo etc assembly is indicated on the diagram...just to right of top center ...#10 ...you'll see pins numbered and identified as what goes where..hope this helps. #10 is the bike side of the big plug...beside it in the wiring diagram is the actual wiring and pin numbers on the tach/speddo instrument cluster.





Think you can just save these as .jpg to blow them up etc...if not, can e-mail you the .jpg files. Let me know. Good luck

far better than anything I have in my Clymer book. I'll fiddle with the image and see if I can blow it up. Otherwise I will send you a PM. Thanks

This is from a 11/1981 R100RS but the numbers don't change, just which ones connect.