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[Solved] How to test 1982 R100RT headlight relay and left combination headlight switch

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Lee Nyboer
 5499
(@5499)
Posts: 20
Eminent Member
Topic starter
 

I started my 82 R100RT with the head light switch on, saw the light briefly on the garage wall and then go out immediately. I may have even heard a small pop but my hearing is pretty bad at 75... I may have touched the light controls as I started the bike on the stand, but the results following were no low beam, no constant high beam, but the high beam passing flasher still working. The Osram Bilux H4 lamp (60/55W) tests good on high and low beam and I've never had a high watt bulb other then this in the lighting system. I've read Snowbum's and Oak's input on the complexities of the 81-84 R100RT headlight system and an electrical Guru I am not!! I do have a 12V test light and a good Multimeter.

What I'm looking for is a guide to see if the left bar lighting controls (mainly headlight rocker switch) can be tested to see if the contacts are still functioning properly or Fried! The switch (61 31 1243731,732,730) show unavailable at Bob's Motorcycle so knowing it's dead or not is important to what to can do next.

Secondly, it sounds like the Lamp Relay (BMW124305) could also be a part of the problem and how can I test it. This part is available and I could buy new.

With the ignition in start position and w/engine running, passing flasher switch works. All the rear end lighting works as do the turn signals. Also, the eye brow parking light works with the 3 position selector.

where do I start!

 

 
Posted : 11/15/2023 19:34
Richard W
(@wobbly)
Posts: 2558
Member
 

First look at the 2 fuses. REPLACE the entire OEM fuse box with modern, flat-pack fuse holders. Like below. Then install two 10A fuses.

 

?1

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 11/17/2023 06:27
Steven Rankin
(@14724)
Posts: 204
Estimable Member
 

So yes, you can check things with a probe and multi meter.  

NO, you don't have to fool around changing fuses from factory to OM.  Anytime you change the factory wiring unless you are a VERY good electrical person, you are just asking for problems.   I don't know why people say to do that not realizing or making it clear how much of a job it is to do.  And it is NOT that difficult to change the factory fuses, it is not like they blow out regularly. If they are, there  is a problem to be found out.

Anyway, back to the problem.  The headlight is not a fused item, if you are getting a lighted headlight with the flash switch IT IS NOT A FUSE.  IF the light were fused, a blown fuse means you would not get ANY light.

The bad news is most of the wiring stuff is stuffed inside your headlight shell and if you have had the headlight out, you can see it is pretty tight space to work in.  The terminal ends for the headlight switch end up in this bundle of snakes attached to the white circuit board.  Also from there there are a couple of wires going to the headlight relay.

At this point, do you have a good wiring schematic?  I don't have mine handy at this time but I can perhaps get a look to see just what wires to poke and check.  

For now, do something simple, get a bit of contact cleaner and spray inside the switch as best you can.  

By the way, I capitalized points not for you as the original person asking the question but to make it clear to those who should know what is going on.   I have to finish my coffee and get out to the shop, perhaps in an hour or two I can have a better idea how to proceed. St.

Beware! I do not suffer fools gladly! St.

 
Posted : 11/17/2023 07:36
Lee Nyboer
 5499
(@5499)
Posts: 20
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Topic starter
 

The two dash fuses (and only fuses I can find) are 8 amp and both are good.

 
Posted : 11/17/2023 07:43
Lee Nyboer
 5499
(@5499)
Posts: 20
Eminent Member
Topic starter
 

The clymer diagrams are sort of OK and is what I have. It’s a mess in the bucket, but if I’m reading it correctly:

YW at relay to Y on the circuit board or headlight runs through the low beam switch and should show continuity. 
YW at relay to W on circuit board and headlight should show hi beam continuity.

 

 
Posted : 11/17/2023 08:48
Steven Rankin
(@14724)
Posts: 204
Estimable Member
 

The green wire is a switched hot wire.  You should get a voltage reading at pin 56 the white wire at the circuit board for high beam. The white wire exits the switch goes to the circuit board from there directly to the bulb and high beam indicator light on the dash. Thing get funny at the yellow wire or low beam side of things.  On one side of the board it is res, and green wire.  Opposite is Yellow 56b. that should have power.

LOL, from what I see, if you have power at 87b on the relay, it is working?  Looks like the yellow white wire may control the relay.

So my guess is if you have continuity between the green wire and yellow wire in the low beam position that part of the switch is good.

When engaging the high beam the yellow white wire is energized to operate the relay and there should be power from the green to white wire on the switch as well as at the yellow white.

I hate to say but  there is a pretty good chance the relay is shot.  Unless switches are exposed to real harsh conditions or are high mileage lots of use they seem to be pretty robust.

LOL, I hope I haven't confused you more or been unhelpful.  Over the years I have found trying to troubleshoot an electrical problem via the forum to be highly frustrating at tunes due to the limit imposed by this means of communication.

At times like this I usually ask where are you located?  Not to far and I am always willing to stop by.  Good luck, St.

Beware! I do not suffer fools gladly! St.

 
Posted : 11/17/2023 09:27
Lee Nyboer
 5499
(@5499)
Posts: 20
Eminent Member
Topic starter
 

Thank you Steve, I will confess I am a bit confused by what you wrote and thought I might try and isolate just the Hi Low beam switch to check continuity. My WY wire removed from the relay connected to the W high beam lamp plug showed continuity and cut off when I moved the switch to low beam. The same WY connected to the Y low beam at the headlight also responded properly to the continuity when I switched in and out of low beam. I therefore suspect as you have stated that the relay is a likely problem. So, I will order a relay and see what happens. I believe parts of the relay are working fine and others are not. 87B (Gray)is providing power to the dash lights and tail lamp & Running lights but 87 YW is not receiving power and it looks like the switch is good on the handlebar. I’ll see if I can check the voltages as you had stated. Thanks for the help.

 
Posted : 11/17/2023 11:08
Steven Rankin
(@14724)
Posts: 204
Estimable Member
 

Yes, your write up about the action you are seeing with the yellow white wire makes sense.  The low beam as far as I know on your bike unless it has the three position headlight switch on the left side, is always on.  It is tied through the ignition key and relay to switch the low beam off when the starter is engaged.  

Yeah, even as simple as the wiring is on the bike, if you don't work with it a lot it can get confusing.  Just a note, I think over 39 years I have replaced four headlight relays, and until a couple of years ago when I did a complete overhaul of the bike, I had the original switch gear on the left side.  As during the last overhaul, I installed all new wiring harnesses for some crazy reason I changed out the original switch to a brand new Euro switch.  So LOL four relays, zero switch failures in 37 years 220K miles.  I ride all year round in Rochester NY weather and despite the salt, I feel that is pretty good testament to just how robust the OM switches are.  Then again, LOL I have seen them fail in 34K miles.

Let me know if the new relay solves the problem.  Good luck St.

Beware! I do not suffer fools gladly! St.

 
Posted : 11/17/2023 13:25
Lee Nyboer
 5499
(@5499)
Posts: 20
Eminent Member
Topic starter
 

Dave Alquist of Quality Cycle Service sold me a used relay where BMW US and Canada have none (600 in Germany and 3/4 week’s delivery). I do have the 3 position light switch off, parking & on . I’ll post my results when known. Thanks for the help. Lee

 
Posted : 11/17/2023 15:41
Richard W
(@wobbly)
Posts: 2558
Member
 

Posted by: @5499

The two dash fuses (and only fuses I can find) are 8 amp and both are good.

I didn't say the fuse was bad. In my experience these type fuses simply make VERY poor electrical contact. That's why ALL the German cars and motorcycles stopped using them decades ago. 

I agree. Most of the Airhead wiring is superb, the one glaring weak spot is the fuse holder. If you want modern reliability from your older Airhead, then you're going to need to update the fuse holders. (If you want to troubleshoot your electrical system, the place to start is by insuring a constant electrical source. That is common sense.)

Additionally, you will not find the older type German fuses at your average filling station anywhere in "small town USA" during your travels. So if you happen to blow one of the older fuses, you may be up a certain polluted estuary with no visible means of propulsion. 

And on top if that, getting to the fuses on a pre-1985 RT or RS on the side of the road is a royal PIA. 

Anyway, back to the problem.  The headlight is not a fused item...

Excuse me, but all lights are fused, through the fuse on the Gray & Gray/Black wiring.

 

So I'm afraid Steve's advice to you is WAY off track on these points. 

 

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 11/18/2023 16:30
Lee Nyboer
 5499
(@5499)
Posts: 20
Eminent Member
Topic starter
 

I’ll consider changing the 2 fuses. I have a supply of these that I’ve used in my boat. My glass fuses are located at the top of my dash and are easily accessed by not being in the lamp bucket.

 
Posted : 11/18/2023 17:44
Steven Rankin
(@14724)
Posts: 204
Estimable Member
 

If you are not implying it is the fuse, why in the world are you writing about changing the fuses and holders?

5499, are you writing the fuses on your bike have already been changed at one time?  If so, ignore my rant, someone already changed the holders and it is too late to go back. What are you using now?  If it is working don't change it. The less you change the better.

I will say it again, changing the fuse holders on an airhead is nonsense and NOT needed.   There is NO data to say the "new" fuses are any better than the old fuses.  

Yeah, modern fuses are easier to change and designers finally figured out how to make the fuse easier to change and even in some cases in modern vehicles easier to access.   Someone finally listened to the consumer or mechanics.  

A fuse is a fuse the only reason people change the fuses in airheads is for some cockamamy reason they think it so hard to change the original fuses when one blows.

First, if you are blowing fuses figure out why.  The ONLY times I have blown fuses on my bike is when I am directly working on wiring such as when I changed the turn signals on my RT from plastic to aluminum.  Or, I added fog lights.  

In normal use of the bike you should only change fuses infrequently.  I haven't changed a fuse in my RT now in two years or more. Never in any of my cars since I tried adding fog lights to a 71 Chevy.

Second, most people I have come across that changed fuse holders can't solder or do a poor job.  And just add to their electrical problems.   Why bother when the OM fuses work?  The less you mess with the OM wiring the better off you are.

And I am sorry if I am insulting someone's soldering or electrical repair skills but frankly the majority of people have issues. if you are in the minority forgive my rant. 

 

Beware! I do not suffer fools gladly! St.

 
Posted : 11/19/2023 06:26
Richard W
(@wobbly)
Posts: 2558
Member
 

Posted by: @5499

I’ll consider changing the 2 fuses. I have a supply of these that I’ve used in my boat. My glass fuses are located at the top of my dash and are easily accessed by not being in the lamp bucket. 

• Remote fuses for the RT and RS was considered an "upgrade" back in the 1980's. In fact my 1979 RT came with both holders remoted to the a location near the tool tray by the previous owner. However, telling some one "this is a good thing" in a newsletter (remember monthly newsletters?) and the owner's execution is usually 2 different things. My engineering career was spent working on military grade electronics, so I know good wiring when I see it. My RT's remoting was accomplished with regular household lamp cord and electrical tape. This is far less than optimal. All motorcycle wiring needs to be done with "automotive wire" and have soldered connections that are then protected by heat shrink. Hopefully it should match what's under the hood of any new car as far as connection quality, waterproofing and scuff/UV resistance. 

• You mentioned "glass fuses" and more alarm bells went off. 1) Do you mean the older, American type of glass automotive fuse? And, 2) are you therefore inferring the use of of the spring-loaded in-line fuse holders common to motorcycles in the 1980's? Like this...

From a reliability and performance standpoint the worst fuse style is the German style, and the second worse is the spring-loaded, in-line glass fuse such as the one shown above. The contact pressure and surface area are simply not large enough. And we won't even mention water fouling with dis-similar metals.

The one thing you are trying to nurse from your 40 year old Airhead is some semblance of reliability so you can take a 350 mile day ride. When you answer these questions, and/or show some photos, I'll show you how to quickly and easily convert your fuse holders to something relevant in the 21st Century.

Regards

 

This post was modified 8 months ago 2 times by Richard W

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 11/19/2023 08:51
Lee Nyboer
 5499
(@5499)
Posts: 20
Eminent Member
Topic starter
 

I haven’t seen this fuse arrangement on any microfiche showing 1982 R100RT electrical parts. Perhaps this fuse upgrade was done prior to me owning the bike but I don’t see any porcelain fuse fixtures on the top corner of my connection board in the back of the light bucket which lead me to think it was original. It seems to be a good arrangement and takes standard 313 AG 8A 32V  1-1/4” glass automotive grade fuses which are available in the US. I carry 6 spares and have never blown one yet.

 
Posted : 11/20/2023 07:46
Lee Nyboer
 5499
(@5499)
Posts: 20
Eminent Member
Topic starter
 

I haven’t seen this fuse arrangement on any microfiche showing 1982 R100RT electrical parts. Perhaps this fuse upgrade was done prior to me owning the bike but I don’t see any porcelain fuse fixtures on the top corner of my connection board in the back of the light bucket which lead me to think it was original. It seems to be a good arrangement and takes standard 313 AG 8A 32V  1-1/4” glass automotive grade fuses which are available in the US. I carry 6 spares and have never blown one yet.

 
Posted : 11/20/2023 07:46
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