85 BMW R80RT Headlight problems

[franko]

On my bike the low beam had gone out. Just getting by with high beam for a short while. It also went out.
I took the headlight apart figuring that the old LED system went bad. I have a new one for it. Plugged in the new one, only high beam. Plugged old one back in, only high beam.
Brought out the multi meter. Set on high, Yellow to brown 12.10 volts. Y to white 12.10 volts. B to W 0 volts. On low beam the measurements are Y to B .01 V. Y to W .01. B to W .00.
Looking in the Clymer manual for BMW edition M502-3, on pages 784 to785, it shows Brown as being the ground wire. From the readings I took, it looks like Yellow is acting as ground.
The schematic also shows the yellow wire from the headlight connecting to “Crt board contacts”. Is this between the speedo/tack? As I tried to figure out what it was, the best I could do is the drawing on page 430 of the same book.
If that is the problem, would a Catdash system be a good choice for replacement.
Any and all information is appreciated. If I need to dig into it to far, I will just put it back together and run on high for now. It’s not as bright as new car low beams. I want to be able to go on one more lunch run with my son when he can fit it in.

 

[20774]

Usually when there's weird headlight problems, I typically would look to the light relay...should be in the headlight shell. And my older Haynes indicates that the brown wire is ground...that's pretty typical with BMW and their diagrams.

 

[stevenrankin]

Relay

I believe your relay is under the gas tank along with most of the "circuit board"? If not, the inside of your headlight shell would be full of jumping snakes. I will see if I can dig out a schematic and see if I can make sense out of things. Sorry, I am not fully experienced with your year bike.

Frankly while I hate swapping parts to fix things, most likely you either have a bad connection or a bad relay. That is only a wild guess. Good luck. St.

 

[pglaves]

I am not sure why a yellow to white test would show positive voltage. I would expect it to be open unless the low beam is grounded somewhere. Relay? I am not sure but would not expect to see ground at the low beam wire.

 

[James.A]

The one and only time that ever happened to me, it turned out that the voltage regulator was no longer regulating. The alternator was delivering as much as 16 volts to the system at higher RPMs. The bike is an R75/5, but the electrical system, if stock, is pretty much the same. The test is to clip leads from your volt/ohm meter to the battery on the volt setting and start the motor and wind it up. The voltage reading should climb to around 14 volts and stop there. I find a meter with a sweep hand to be ideal for this test. Having owned BSA's before BMW's, this fault was very familiar to me. In ancient times, a battery cell going dry was also an indication.

 

[franko]

Thank you for the suggestions.
Some relays are under the tank by the coil. One I think is the starter relay. Another one that I don't know. It has 4 wires to it. Blue, Blue, Black and Brown.
Another relay has the number printed on it 89 9675 and connection numbers 30, 85, 86, 87, 87B. The wires going to it are Purple,Green. Grey. Red. Yellow,black. Black Grey.
The other relay just has connection numbers on it. 30. 85. 86. 86A. 87. The wire colors are Brown,yellow. Blue,Green. Black. Black. Brown,Blue. Brown,Black. Brown,Black.
These colors and number of wires don't exactly match what is in the Clymers book.
If a educated guess was needed, which one was for the headlight, I will replace it to see if it helps.
Somewhere in time, I have seen schematics that had the connection numbers called out. I would like to find those drawings again.
Thanks again

 

[Omega Man]

This may help- https://forums.bmwmoa.org/showthrea...stem-Wiring-and-Components-Resource-Materials

OM

 

[stevenrankin]

Eme

I have found the best available schematics for sale at EME. They are large, in color with relay pins numbers. all the good stuff labeled. they are plastic laminated and very durable.

Be aware however they may not be the be all end all needed. BMW in some cases makes changes to wiring without updating schematics. So I have collected Clymer, Haynes, EME as well as factory schematics for the two bikes I have as well as auxiliary one for hazard flashers and heated grips.

I haven't been in the garage yet to look at what I have for your bike. St.

 

[franko]

Thank You, I will look into it.
I'm going to get my cane, shake it at the clouds as I stand on the front lawn remembering this
https://i0.wp.com/granttiller.com/wp-content/uploads/2022/02/1-Pre-1971-Commando-Original.png?ssl=1

 

[stevenrankin]

What I have found

So looking in my New Haynes book with the now color schematics I see the headlight relay marked and colored as such. I do see a BIG difference in the Clymer manual for 85 RT, In my Clymer, 84 R80RT and 85 are lumped together with a schematic I would expect for my 84R80RT. It isn't until I look at the Clymer book further there is no schematic for the R80RT that matches the Haynes. The only schematic I have in Clymer that matches the Haynes schematic for 85 R80RT, is for the 100RT??? Maybe I am blind but I don't see another R80RT schematic other than the one???

Going by the Hanes Manual;
Pin 86 Green/gray (sorry I can see so well so I am assuming it is Gray). On the UK models that wire goes to the switch on the handlebar. US models shows it jumped to Black Yellow. At a connection bar of some sort. (again I am sorry I don't know a lot about your bike as to where this is)

Pin 85 Black, this goes to the starter relay

Pin 87b Gray, along with Gray/white. (Gray/white is for RT models). Gray/white goes to one of the fuses pin 58. Gray and Gray/white go quite a few places.

Pin 30 Red

Are you able to follow this from here? I am cross eyed trying to follow Gray and Gray/white. Good luck, St.

 

[guenner]

LED system went bad

Means you are using LED light bulbs?

 

[stevenrankin]

Led

LOL, did you try switching to a halogen bulb? St.

 

[franko]

I typed this out before. Hopefully I will get it through.
20774: I think it is the relay with the 87b on it. I'm not sure yet.
Stenenratkin: at $60 plus shipping, I'm not enthused about parts swapping either.
PGlaves. The yellow is acting as ground for both low and high beam. It has me scratching my head. Also the brown isn't acting as a groung
James A. The voltage reading is 13.5 volts at 3,500 RPM.
Omegaman: With Brooks article, most, not all, of the pictures won't show up on my laptop.
Stevenrankin: I bought a replacement ignition from him several years ago. Looks like time to place an order.
Stevenrankin. Thanks for the wiring information. I will need to write it out on a card and try to follow it.
Guenner: I bought a LED unit for my Norton. The BMW bulb burned out so I used the LED unit it it. It worked well. It had been in for around ten years or more and around 35,000 miles. I liked it so much that I ordered another one for the Norton and a second as a spare. It is plug and play.. It looks like a small transformer and a small fan attacked to the backside of the bulb.
Stevenrankin: I do doubt that I would go back to a halogen bulb.

 

[pglaves]

PGlaves. The yellow is acting as ground for both low and high beam. It has me scratching my head. Also the brown isn't acting as a groung

You have identified the problem. Now to identify what has caused the problem. Brown is the ground wire. You need to trace it until you find out why it is not grounded.

It is possible that yellow (the low beam circuit) is grounded some place. You need to find where it is grounded. It might simply be through the relay or bulb.

ADDED: Often when a circuit lacks a proper ground the pesky electrons will find whatever path they can find with the least resistance.

 

[stevenrankin]

Schematic

One of the things I want to stress that I found while digging in my garage is there is more than one or maybe only one schematic for this bike.

It gets to be a royal pain sometimes trying to trace what is going on in a wiring system when the schematic is not quite right. So before you drive your self nuts, confirm what you have, and get the schematic to go with what you have.

Again and I am not making a commission but the best schematics so far are from EME. Having colored wire on the drawing is a nice item, having the pins marked on the relays can be a great thing.

I will admit, my Haynes manual schematic is confusing as it not only shows US but UK configuration of the lighting system.


LOL, it is a lot easier having the bike at hand when trying to help someone with wiring. Let me know what the wiring configuration is on your headlight relay and I will dive into my schematics and see if I can figure out what the electrons are up to or not. St.

 

[guenner]

According to the diagram the high beam is the white wire and and low beam is the yellow wire.

If you measure the voltage between the yellow wire (active with 12V) and the white wire you get about 12V because the test finds ground through the high beam bulb.

 

[franko]

Short version---It was the handle bar switches.
More details:
I found a place not too far away that had the headlight relay in stock. As Mitchlers and Kurts have left the business, on the shelf Airhead parts are scarce. Thoroughbred Cycles by Elkhorn WI had it. I put the new relay in and the same thing. Started pulling on wires to try to trace where the runs went. Sprayed carb cleaner on the wires so I could clearly see the colors. Now it's back to no lights, as it was when the story started. Flipping switches and cutting wire tape off in places to look for crushed/broken wires. Now I have low beam. Only. Put in old relay. I have low beam. put in old bulb I have low beam. So thinking back words, the only thing that I haven't worked on that is part of the system is the handle bar switches. I took off the hand guard and then took apart the assembly. I didn't take the switches apart because..........well experience. I sprayed electronic cleaner into the switch assembly several times. Reassembled it and all systems worked. I would like to find a Penetrating Dielectric grease to spray into the switch gear. I took it for a 10 mile ride to see if it would stay working. Yep.
I would like to thank all of you who helped by replying as that is what kept me going and not saying "I'll get to it over the winter"
Again Thank You.

 

[stevenrankin]

Another bit of information for the next time

I am so glad you found the solution and that it was not a big expense to fix. I am also thankful you have taken the time to share the fix with us. You never know it may happen to someone else and it is a simple thing to try first. St.

 

[franko]

I am sincere in my gratitude for the help. Every suggestion was one more thing to eliminate from the list of what could be wrong. It kept me going, instead of being frustrated. Thanks to EVERYONE. Frank Coleman

 

[franko]

I took the handle bar switch apart today. I was able to buy Dielectric grease in a spray can. It acted like a penetrating grease, but was not called out as such. https://www.farmandfleet.com/produc...MI1vjv8L_sgQMVGBOzAB0AJwjaEAQYAyABEgLva_D_BwE To me as I sprayed it, it reminded me of https://www.spsindustrial.com/penet...MIvK2RhsDsgQMVQsnjBx0uwwqyEAQYAiABEgIb2PD_BwE Zep 2000. As I reassembled the switch, the solidified grease was leaking the the outside of the housing. The turn signal needed a little extra extra help after the cleaning by the electronic cleaner. Now all is fine. Good luck and thanks again for the help.