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no low beam headlight


MontanaBud

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2004 RT 128k

 

On a recent trip the general warning light came on a few times and I found it was attributed to a sticking foot brake micro switch. A few weeks later, on another trip, the general warning light returned, again related to the sticking switch, but as before the warning cleared up on restarting. A day later I found the low beam headlight burned out. When I replaced it, I go no light and had to rely on the fogs to get home.

 

The tail brake and running lights are fine. The high beam, fog and pilot lights all work. No odd display lights shown (i.e., no high beam indicator on when it's not on).

 

I've pulled the nose off (upper fairing), and examined the wiring inside the headlight, and as far as I can see it all looks like new. With a voltmeter I checked the plug socket for the headlight on the bike, and there's no power there to the low beam yellow wire, so I'm fairly confident the problem is not inside the headlight.

 

I bought and installed a used left handle bar switch, and it made no difference.

 

I'm no mechanic and am particularly inept with electrics. Any suggestions on what I can do, where to look next to fix this?

 

Thanks in advance.

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2004 RT 128k

 

On a recent trip the general warning light came on a few times and I found it was attributed to a sticking foot brake micro switch. A few weeks later, on another trip, the general warning light returned, again related to the sticking switch, but as before the warning cleared up on restarting. A day later I found the low beam headlight burned out. When I replaced it, I go no light and had to rely on the fogs to get home.

 

The tail brake and running lights are fine. The high beam, fog and pilot lights all work. No odd display lights shown (i.e., no high beam indicator on when it's not on).

 

I've pulled the nose off (upper fairing), and examined the wiring inside the headlight, and as far as I can see it all looks like new. With a voltmeter I checked the plug socket for the headlight on the bike, and there's no power there to the low beam yellow wire, so I'm fairly confident the problem is not inside the headlight.

 

I bought and installed a used left handle bar switch, and it made no difference.

 

I'm no mechanic and am particularly inept with electrics. Any suggestions on what I can do, where to look next to fix this?

 

Thanks in advance.

 

Afternoon Bud

 

There is more to that headlight circuit than on the L/H switch side.

 

The LOW BEAM (B+ 12v) power flows through the R/H side switch pod then across to the L/H side, then to the headlight.

 

Any chance that your bike has the European low beam on/off switch added (many were converted), it would be on the R/H side switch pod? If so then make sure it is turned on.

 

If no European headlight switch then you will have to trace the power to the R/H side then across to the L/H side hi/low switch.

 

The 12V goes into the R/H side on the Green/Blue wire & comes out on the White/Yellow wire then goes across to the L/H side on the White/Yellow wire (does the White/Yellow wire have 12v power going into the L/H side hi/low switch?

 

 

 

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Thanks. Those wires are sealed and exceedingly small. How does one test for voltage in the white/yellow wire without a needle probe?

 

I have a test probe but now can't seem to locate a white/yellow wire. Could it be a different color?

Edited by MontanaBud
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The wires going to the r/h switch are brown, blue/brown, blue/green, yellow/brown, blue/brown, yellow/brown, white, and green/yellow. The white does have power.

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The wires going to the r/h switch are brown, blue/brown, blue/green, yellow/brown, blue/brown, yellow/brown, white, and green/yellow. The white does have power.

 

Afternoon Bud

 

See if you have 12v power entering the hi/low switch on the L/H handlebar pod, you should also have 12v coming out of the switch on the yellow wire.

 

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Hmmm. I was certain I had power on the white wire to the left hand switch (I mistakenly said r/h above), but today I got no signal with the probe on the white (key in on position), but the high beam switch does sends power to the headlight plug-in on the bike, the horn works, as does the windscreen adjuster. When I probed the yellow wire, it set off the hazard lights, and when I probed the blue/yellow wire, it sounded the horn.

 

What can we make of this?

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Hmmm. I was certain I had power on the white wire to the left hand switch (I mistakenly said r/h above), but today I got no signal with the probe on the white (key in on position), but the high beam switch does sends power to the headlight plug-in on the bike, the horn works, as does the windscreen adjuster. When I probed the yellow wire, it set off the hazard lights, and when I probed the blue/yellow wire, it sounded the horn.

 

What can we make of this?

 

Evening Bud

 

The high & low beam both feed off of the same supply wire coming from the R/H switch pod, the flash-to-pass feeds off of it's own separate supply circuit.

 

The low beam taps it's power before it gets to the L/H switch (white/yellow wire).

 

So if you have high beam then you must have 12v at least as far as the L/H switch.

 

Are you sure that you don't have 12v at the yellow wire at the rear of headlight? If (positively) no power to the yellow wire at rear of headlight but you do have power to the L/H hi/low switch then you probably have an open in the yellow wire, or an open at the splice joint.

 

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With the high beam turned off, there is no power to the socket that the headlight plugs into on the bike frame (checking pins in front, and wires in rear of socket). There is power to one of the pins when the high beam switch is in the on position, but not otherwise.

 

Splice joint? All the wires seem to run into the tightly wound loom. A dead end for me.

 

On reflection, I did notice on the trip that my clock was off from the correct time, so must have lost power at some point (oh, gremlins!). On my last ride, I noticed the speedometer was bouncing irrationally, then settled into what appeared normal operation (never done that before). I suspected that may have been related to some oil seeping from the left fork leg seal. Would these have any relevance?

 

Thanks again, DR.

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I don't feel a click on the #10 relay when I turn the key on. Normal? I swapped the relays and no difference, so I'm assuming the relay itself is fine.

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I don't feel a click on the #10 relay when I turn the key on. Normal? I swapped the relays and no difference, so I'm assuming the relay itself is fine.

 

 

Evening Bud

 

Relay 10 is the flasher unit, relay 4 is the load relief relay.

 

Probably doesn't matter as IF your high beam is operating then your relay is OK.

 

 

 

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My BMW repair manual pdf shows this:

 

61 31 Relay positions/fuse assignments

(central electrical equipment

box)

Relay positions

1. Flasher unit

2. Indicator damping

3. Coded plug for Motronic (not used)

4. Starter motor relay

5. Relief relay

6. Horn relay

7. Fuel pump relay

8. Motronic relay

9. ABS warning relay

10.Lighting relay

 

I might have the wrong edition? Plus, I have no idea what a relief relay is!

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My BMW repair manual pdf shows this:

 

61 31 Relay positions/fuse assignments

(central electrical equipment

box)

Relay positions

1. Flasher unit

2. Indicator damping

3. Coded plug for Motronic (not used)

4. Starter motor relay

5. Relief relay

6. Horn relay

7. Fuel pump relay

8. Motronic relay

9. ABS warning relay

10.Lighting relay

 

I might have the wrong edition? Plus, I have no idea what a relief relay is!

 

Morning Bud

 

The lighting relay is for the fog lights.

 

The load relief relay (relief relay) is what controls the hi / low beam.

 

Your book just lists the relays in a different position than my BMW wiring manual does.

 

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Okay, thanks.

 

I see two side-by-side relays (or what look like relays) under the tachometer. Any idea what those are for?

 

Also, have you ever seen such thing as a non-contact DC voltage detector? Several for AC available, but I can't find one for DC.

Edited by MontanaBud
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Evening Bud

 

I see two side-by-side relays (or what look like relays) under the tachometer. Any idea what those are for? ---Are they factory or something that was added by a previous owner? Probably need a picture here to tell you much.

 

Also, have you ever seen such thing as a non-contact DC voltage detector? Several for AC available, but I can't find one for DC. --Yes, no, sort of. You can put a load on the DC wire (like a light bulb) then put a standard turn signal flasher unit in where the circuit fuse is (that should flash the DC power). Then a standard compass moved along the wire will sometimes show the failure area.

 

Mostly for DC troubleshooting I just use a standard 12v test light then probe each access point along the circuit starting at the fuse (or power source) then working through each connector & switch to find where the power flow fails.

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