USA vs UK headlight relay

[bbelk]

I just spent a painful 6 hours installing a new left side set of switches that cost an incredible $178. The weirdness is that my old setup did not have an on/off switch for the lights and the new one does. It would have been easy enough to isolate the wires coming from the switch and just let them hang, but I didn’t go that route.

The new switch has three positions. One is labeled off and in this position, the lights are off. As wired from the factory and according to the diagram below, the other two positions result in all of the lights being on. In the middle position the lights get their power from the fuse panel (area 58) via the new left side switch. In the bottom position, the lights get their power via the headlight relay. There is no functional difference in these two switch positions except for the routing of the power.

Is this how it works in the UK?

It would seem to me that the headlight circuit should be separated from the Parking light circuit somehow, but they are clearly joined together via a Spade lug splitter on the headlight relay (87 and 87a).

This would not be an issue for the USA version with the always on light relay, which leads to my actual question.

Is the headlight relay different on USA vs UK bikes?

The design would work with a diode between the fuse panel and headlight relay or by using a double pole light relay. Neither of these is shown in the diagram below. I couldn’t find a diode so I added a second single pole relay and made an already crowded headlight bucket even more crowded.



Lower left portion:



Upper Left Portion:

[melville]

Ignore the black wire. Just put the brown wire on #85 and be happy. That has to be an error in the Haynes diagram.

I can't figure out what the black wire would do, as where it is it's disconnected most of the time and would be a redundant hot when the starter is engaged. You need hot going in to #86 and #85 connected to ground to make the relay work.

See my build thread for more relay fun!

If all the lights are on in position #2, including the headlight, you have the wrong relay. The right relay has two separate internal switches for #87 and #87b. The wrong relay has one internal switch and #87 and #87b connected internally. This allows #87b to supply power to #87.

The idea here is that headlight draws should only go through the relay, from the red wire. If you are getting headlight in position #2, the headlight is essentially getting its power backfed through the taillight circuit, and none of that power is coming from the red wire.

[bbelk]

The right relay has two separate internal switches for #87 and #87b. The wrong relay has one internal switch and #87 and #87b connected internally.

Yahoo - that is what I came up with after 6 hours of tracking through 35 years of previous (and sometimes creative) previous owners, Haynes, and of course the Germans (that must have a grudge against us). 87 and 87b can't be the same terminal if you have a UK light switch.

Some PO may have changed my light relay or it could be original as it does not matter in the USA configuration.

Anyway - I am sure the right relay costs as much as that switch I just put in so I put in two Merican single pole relays that cost $4.75 each and got to the same place - except for the six hours on the stool, which I wish I had back.

Thanks
Brad

[bbelk]

Today, more fun mit electrons.........

Then I went on to the headlight. I had test fitted it earlier but never powered it up, and it's been out while I chased other electrical demons. After making space in the shell for the lamp, where the US length handlebar switch harnesses make it kinda tight inside when Euro bars are installed, I got it popped in and found that I had a functioning parking light. I also seem to have a passing beam, but I don't seem to have a steady on low or high beam. The bike is pre-1978, and as such comes with a "Euro" light switch, like so:



There are three positions on the switch--top looks like it says "OFF" and then there are two white lines. What should I expect for each position? The lower button is the dimmer, and it appears to work as a rocker switch. When it is held down, it appears to give high beam for as long as it's held (the "passing" beam?). When it's pushed up, shouldn't the dimmer relay get all excited? I'm getting no white hot love form the headlamp system at this point.

I should have re-read your post before diving into this. We ended up in the same place (except for a lot of polishing).

Brad

[Rob Frankham]

Hi guys,

Reading the post, I'm not sure that you've got this sorted yet..

Apart from the switch itself, there are two difference in the wiring between US and UK models.

The first is in the ground wiring to the relay. On the UK spec, there is a brown wire on terminal 85. This is a solid ground and goes to the ground terminals in the headlamp shell. On the US spec, there is a black wire in place of (not as well as) this brown wire. This goes to the starter solenoid and the starter relay at terminal 87. The function here is that, most of the time, this wire is grounded via the solenoid actuation coil which allows the light relay to activate. When, however, the starter button is pressed, this wire is connected to positive volts by the starter relay. When this happens, terminals 85 and 86 on the light relay are at the same voltage (12 volts), thus no current will flow and the relay will drop out (i.e.open). The purpose of this is so that the headlamp load is removed from the battery when the starter button is pressed. This gives more power for starting, It isn't necessary in the UK configuration because the lights can be switched off manually.

The second difference is between the ignition switch and the lighting relay. In the US spec, there is simply a green wire running from the ignition switch to terminal 86 on the relay. This means that, all the time the relay coil is grounded via the black wire, the relay will be activated and the headlights will be on.

In the UK spec, the green wire from the ignition switch goes to the lighting switch then returns from there as a green/violet wire that goes to the relay terminal 86. Again, there should only be one connection to relay terminal 86.

87 and 87b can't be the same terminal if you have a UK light switch.

This isn't, in fact, incorrect.terminal 87 and terminal 87b are both connected to terminal 30 when the relay is closed so both the headlights and sidelights will show. When the relay isn't activated, however (i.e. when the ignition is off) the two circuits are isolated from one another. If this were not the case, then if you were to switch the ignition switch to the parking lamp position, the headlamps would come on.

I hope this makes some sort of sense...

Rob

[bbelk]

Hi guys,.....


I hope this makes some sort of sense...

Rob

It does indeed. I suspect that I didn't have an original equipment light relay as there was only one output terminal which was split externaly into 87 and 87a via a spade splitter.

I fixed this by putting in two relays that work in parallel except that they separate the output terminals when the relays are off.

This was all simple enough once I get there, but it was a long six hours with a tester bent over that headlight bucket cleaning up 36 years of PO wierdness.

I will probably never turn the lights off unless I am working on it or trying to get home with a dead altenator someday. With this in mind, the next time I am in there, I may switch back to the black wire ground. Dropping out the headlight on start up seems like a good idea.

[Rob Frankham]

It does indeed. I suspect that I didn't have an original equipment light relay as there was only one output terminal which was split externaly into 87 and 87a via a spade splitter.

I fixed this by putting in two relays that work in parallel except that they separate the output terminals when the relays are off.

This was all simple enough once I get there, but it was a long six hours with a tester bent over that headlight bucket cleaning up 36 years of PO wierdness.

I will probably never turn the lights off unless I am working on it or trying to get home with a dead altenator someday. With this in mind, the next time I am in there, I may switch back to the black wire ground. Dropping out the headlight on start up seems like a good idea.

Quite so... if the relay only had one output terminal, it wasn't stock.

As a matter of interest, if it had a 87a terminal, it wouldn't have worked either. A terminal marked 87a denotes a NC (Normally closed) terminal while a terminal markes 87 or 87b is NO (Normally Open). You can get (at least) three visually identical relays except for the designation of the second output terminal and they have different characteristics. If there are two 87 terminals, these will be linked permanently internally and will be NO terminals. If one is marked 87a, the relay will be a 'change over' relay and if one is marked 87b, as here, it will have two NO outputs that are isolated from one another when the relay is off. It pays to be quite sure what type you have otherwise the results can be strange and quite confusing.

Again as a matter of interest, most of the later models had the lighting relay linked back via the starter relay (as you suggest) so that the headlight goes out when starting, whether or not they had a headlight on/off switch.

Rob

[bbelk]

if it had a 87a terminal, it wouldn't have worked either. A terminal marked 87a denotes a NC (Normally closed) terminal while a terminal markes 87 or 87b is NO (Normally Open). You can get (at least) three visually identical relays except for the designation of the second output terminal and they have different characteristics. If there are two 87 terminals, these will be linked permanently internally and will be NO terminals. If one is marked 87a, the relay will be a 'change over' relay and if one is marked 87b, as here, it will have two NO outputs that are isolated from one another when the relay is off. It pays to be quite sure what type you have otherwise the results can be strange and quite confusing.

Rob

There is more to learn every day. I didn't realize the 87 lable was some sort of standard - I just thought it was on the drawing. I didn't even look on the relay other than to determine the open/closed states. I got it right so it must have been an 87b - I just wrote it down wrong in the last post.

[melville]

if it had a 87a terminal, it wouldn't have worked either. A terminal marked 87a denotes a NC (Normally closed) terminal while a terminal markes 87 or 87b is NO (Normally Open). You can get (at least) three visually identical relays except for the designation of the second output terminal and they have different characteristics. If there are two 87 terminals, these will be linked permanently internally and will be NO terminals. If one is marked 87a, the relay will be a 'change over' relay and if one is marked 87b, as here, it will have two NO outputs that are isolated from one another when the relay is off. It pays to be quite sure what type you have otherwise the results can be strange and quite confusing.

Rob

There is more to learn every day. I didn't realize the 87 label was some sort of standard - I just thought it was on the drawing. I didn't even look on the relay other than to determine the open/closed states. I got it right so it must have been an 87b - I just wrote it down wrong in the last post.

That's DIN for ya. Chasing stuff on the Airhead is just like chasing stuff on the VW, except the Airhead has a bunch more relays. US and Japanese relays (and other electrical bits) don't necessarily follow DIN numbering.

Just some quickies:

30 is always hot (usually a red wire)
1 is ground (brown wire)
15 is switched on (ignition) hot (black wire)

[Rob Frankham]

That's DIN for ya. Chasing stuff on the Airhead is just like chasing stuff on the VW, except the Airhead has a bunch more relays. US and Japanese relays (and other electrical bits) don't necessarily follow DIN numbering.

Just some quickies:

30 is always hot (usually a red wire)
1 is ground (brown wire)
15 is switched on (ignition) hot (black wire)

Quite right, BMW followed (and still follow) the DIN standard for wiring... well loosely anyway. Not surprising since DIN stands for the Deutsches Institut für Normung e.V. (in English, the German Institute for Standardization). Roughly equivalent to the american ANSI and the British BSI. The standard covers not just terminal numbering but also wire colours.

Incidentally, it's worth knowing that the DIN standard has been changed so later BMWs and other compliant vehicles conform to the newer, different standards. It's also worth bearing in mind that BMW like most other users of the standards, complied only so long as it suited them so, although its a good guide, don't rely on the assignments without checking.

Rob