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Burnt headlight cable on BREVA 1200 (MY 2008)

P

pswiatki

Tuned and Synch'ed
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Do I read the schematic diagram correctly, or the conclusion is utterly wrong: I see no over-current protection in the circuit of the headlight. The current flows straight from the main power bus (generator - battery bus) to the light relay (4 on my diagram) and then directly to the low beam light (56) and through the LH dip switch (9) to the high beam light. If this is true, then I see two major issues: no protection against overcurrent when the generator is producing power (i.e. the engine is running) and the high beam current flows through the dip switch which is also a bit problematic if there is no over-current protection.
I am asking because I just experienced a total burn up of the wires. Fortunately, just past the headlight connector (i.e. closer to the light assembly, 58). The insulation is all gone, individual thin wires split up and caused some secondary shorts, I think.

uc


I ended up with the DSB showing the blue high beam control light constantly (whilst no light in the headlight assembly was operational) regardless of the LH dip switch position (high/low beam) as long as the engine was running. When I turned the bike off and removed the key from the ignition I was surprised to see some other devices (tail + registration lights, my own circuits for the NAV, etc.) still under power and operational. DSB could be also active (I am not sure any more). But all that activity ceased as soon as I disconnected the headlight (at the connector, above in the picture). Needless to say - I removed the battery completely until I sort everything out and make sure I can safely reconnect power.

By the way: it seems pin 4 on the DSB is the sense input for the high beam. If so - It doesn't matter if anything is connected to the headlight connector, right? Only if the high beam switch (LH dip switch) is in ON position? I am asking because I may go for all LED headlight and I just wonder if the bike will be OK with LEDs. I know those are used in the tail/stop lights, so I presume it should be OK for the headlight, too.
 
If we are talking about the B11,
I think the headlight is powered via the fuse on the yellow wire (switches to fuse).
The wire to the generator is a ground.
 
It would help if you confirmed which model this is.
I know on the early Norge there was a possibility of a wire in the headlight getting worn and shorting to the shell.
 
Does B11 acronym stand for Breva 1100? My bike is Breva 1200 (MY 2008) - but the only schematic diagrams I could find are for 1100. Nevertheless, they match the reality on my bike, so I use those. GND is not routed all the way from the headlight assembly to the generator on the diagram I have. So, I am not sure why you mention this.
Main question (which, I believe, is confirmed in other threads) is this:
is there any over-current protection in the [power] circuit for the headlight? I can't find it on the schematics. Very strange if there is no protection whatsoever. I can only see a fuse on the control circuit for the light relay.
 
In the USA, it’s called a 1200 Sport. The manuals are in the DOWNLOAD section.
 
The Breva 1200 has the same wiring as the Norge. Use the Norge diagram. Also the same as the 1200S.
http://www.thisoldtractor.com/guzzi007/schematics/2007_Norge.gif

The headlight gets it's power via the 40A main fuse and the key switch. 24 on the wiring diagram.
The wire to the alternator is the voltage sensing supply to the alternator.
All the grounds go to the frame.
 
Brian, thanks a lot. I actually saw that GIF and got really puzzled while analyzing the headlight circuitry. Had to compare it to the PDF I have (Breva1100_WiringDiagram.pdf) and found a bug in the GIF. Specifically, the original is:

uc


This is wrong - the blue wire is GND ground and it looks as if it was common only to both front turn indicators (54, 59) and the low-beam light (56). What about high beam 57 and parking light 55? It would be extremely odd to have one light controlled from the high side (+12V) while other from the low side (GND), so it had to be an error.
Correction should be made (and it matches the PDF):

uc


Now it all makes sense as everything is high-side controlled.
As far as the over-current protection is concerned: well, it is not only the headlight that is powered from that main power bus (with a 30A fuse in my case) and the headlight happens to have relatively thin wires for the current they have to conduct. So, no wonder they burnt when some kind of a short circuit was introduced there. Less than 30A but enough to melt the insulation and do all that damage.
I find this MG design a very bad idea. Shame it was done like that... I mean: it could have burnt anywhere - I guess I am lucky that it did on the "easier" side of the headlight connector, but it could have started inside the wire harness and cause grave damage to all of the electrics in the bike or even a major fire. I will try to fix it by running thicker power wires directly from the source. At the same time, I may replace generator wires as well. We'll see.... The idea of running the power circuit through the handlebar switch is also unfortunate. But it surely saves some money on dedicated relays for the individual front lights.
By the way: can anyone explain why there are two separate outputs from the generator block 28 (I understand this unit on the diagram is the generator + voltage regulator combo?):

uc


I think both outputs are after the voltage regulator? Or I am mistaken?

I understand the red wire is the battery charging circuit. What about the green/black wire connected to terminal G of the generator? Is that the main power bus of the motorcycle?
 
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It looks like the head lights are driven directly from the green/black wire, and the instrument panel provides a ground for the selected filament. I've never noticed this before, but it makes sense.
 
Dave, if you draw this conclusion from the GIF picture - check this one (I fixed the GND routing in the headlight):

had to remove the picture (due to copyright note). But you have the snippet above.

Just to be 100% sure, here is the part of the PDF diagram:

uc


So, I don't think it is anything as bizarre as the DSB switching GND on bulbs in the headlight.
 
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Brian UK said:
The wire to the alternator is the voltage sensing supply to the alternator.
All the grounds go to the frame.
Click to expand...

Oh... I either missed this, or you edited the message after I started answering. Yes, now I see the voltage is supplied to G terminal on the alternator as soon as the key is in RUN position in the ignition. Good to know! Thank you so much.
 
I knew some of those diagrams had errors, but had never noticed that one. The diagram in the workshop manual makes it clear. The blue earth is common to all bulbs, the black is just to the one filament. Don't know if Carl Allison is still correcting them, would be worth trying to get it corrected.
 
If I may ask a quick question: is there any firm cable connection between the engine block and the frame? I know there is one thick cable connecting the negative terminal on the battery with the engine block near the starter motor. What about the frame itself? I would not trust just the mechanical connection between the two (so, essentially all those mighty bolts) for proper current conductivity. But on the other hand, I see GND at the frame near the ECU module, so presumably, such connection (frame-engine block) is somehow ensured.
 
kiwi dave said:
It wouldn't be hard to add another one if you are concerned.
A multimeter set to measure ohms would quickly confirm just how good the existing connection is.
Click to expand...
Thanks! I doubt a multimeter would really show me anything useful - a milliohm-meter would be much better. I agree - it wouldn't be hard to add such a connection, but I thought the factory did it already and I just can't find it in my Breva 1200. If it doesn't exist - sure, I will add it somehow. Unless someone here explains why it isn't really needed.
 
We're dealing with trivia here. Take a voltmeter and measure the voltage between the positive terminal on the battery and the negative terminal, and then the voltage between the positive terminal on the battery and the frame. If they differ, then you might have a grounding issue.

Otherwise, why worry?

My last post on this subject, I have better things to do.
 
Thank you much for your time, Dave. Alright. I will do it, check the voltage difference. It is interesting how you approach the issue:
kiwi dave said:
If they differ, then you might have a grounding issue.
Click to expand...
How can this happen? Engine loose in the frame, or what? This was exactly the uncertainty I had and the reason why I asked the question above.

You see: trivia or not - my bike almost burned completely and is now totally disabled. I have to replace the entire harness (which is not immediately available and the store will have to source it - most probably directly from MG factory - so I will have to wait for weeks until I get it). I want to go to this extreme measure because I don't know how far inside the harness the damage went. For now, after taking off the headlight, I know most of the wires in the area between the headlight and DSB are damaged and will have to be replaced. Probably also several connectors which melted to the point where I cannot disconnect them anymore. So, I will be forced to cut those off and replace them with something. Also, since the headlight wires that come out from the main harness further away from the DSB are also damaged, I presume there is damage inside the harness as well. I just don't trust anything there anymore.

Therefore - since [almost] all of the wirings will have to be replaced on the bike - I will also try to remove the weak points. But I have to identify those. Some of them are obvious, others are not. I know for a fact the primary reason was a short-circuit of hi-beam to ground inside the headlamp and it caused all the damage around. It is a very bad design on MG part, this much I already know. Learned the Hard Way :oops:
 
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