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Old 04-17-2013, 06:51 PM   #1
Noswal OP
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Joined: Jun 2009
Oddometer: 81
Headlight/Relay Question

My bike is a 1975 R90S.
I went for an amazing ride this evening and arrived home just as it was beginning to get dark. When the headlight of my bike failed to throw any light into the garage I knew something was up.
The parking/running light was working- however no high/low beam. I dropped the fairing and popped the bulb and replaced it with a used extra H4 that I had lying around. Same thing with the other bulb- no high/low but this time I hit the passing light and the headlight came on full bright. So, I'm assuming that perhaps it's the relay? Hopefully one of you might confirm this...
If it is, which relay is the headlight relay? I'm looking inside the headlight, and the relay that appears most likely (to me) is the one at the 4 o'clock position. Also, adding to the confusion, I read online that the purpose of the relay is to simply kill the headlight while the bike is started- which might leave me to believe that it's not the relay- but this might only apply to later bikes...
Thanks for your help- Jim
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Old 04-17-2013, 08:41 PM   #2
bmwrench
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You are looking at the correct relay. It's main function is to handle the load that the small light switch should not. Check for power at the yellow/white lead with the ignition and light switch turned on. The relay should also click audibly when the light switch is turned on. At this point, you don't know whether the relay or the switch is the problem.
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Old 04-18-2013, 04:45 PM   #3
Plaka
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Quote:
Originally Posted by Noswal View Post
My bike is a 1975 R90S.
I went for an amazing ride this evening and arrived home just as it was beginning to get dark. When the headlight of my bike failed to throw any light into the garage I knew something was up.
The parking/running light was working- however no high/low beam. I dropped the fairing and popped the bulb and replaced it with a used extra H4 that I had lying around. Same thing with the other bulb- no high/low but this time I hit the passing light and the headlight came on full bright. So, I'm assuming that perhaps it's the relay? Hopefully one of you might confirm this...
If it is, which relay is the headlight relay? I'm looking inside the headlight, and the relay that appears most likely (to me) is the one at the 4 o'clock position. Also, adding to the confusion, I read online that the purpose of the relay is to simply kill the headlight while the bike is started- which might leave me to believe that it's not the relay- but this might only apply to later bikes...
Thanks for your help- Jim
Yes, it's a load shed realy. look closely at your wiring diagram. power to the starter solenoid acivates the NC relay and kills power to the headlight. if the relay sticks the power is cut all the time. or their can be a wiring fault. I'm working on making mine vanish, permanently. Essentially you jumper it out of the circuit and throw it away. One less thing to screw up. Simple enough to not turn on the headlight when starting. (The lack of a headlight switch got dealt with too).

You can jumper around it temporaritly to test it. Or pull it and bench test it.

The big green box is the flasher. You can hear/feel it clicking with the turn signals. The silver goober is the headlight relay.

With teal halogen bulbs it's worth fitting a real headlight relay (a pair of them) to take the load off the switch.
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Old 04-18-2013, 08:46 PM   #4
bmwrench
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The headlight relay is only connected to the starter relay from '78 on. On his bike a green wire powers the relay coil. The starter relay lead is in the harness in the headlight and can be connected if one desires.
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Old 04-19-2013, 05:38 AM   #5
Noswal OP
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Fixed-

Thanks Plaka and BMWwrench. Determined that it wasn't the relay and last night went about replacing the switch from a donor bike that I'm lucky to be able to scavenge from. It's a little intimidating pulling wires inside the headlight but all-in-all, it went fine.
Anyhow, the lights are now back on. Appreciate the assist.
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Old 05-03-2013, 09:35 AM   #6
Fritzie
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Me too

Quote:
Originally Posted by bmwrench View Post
You are looking at the correct relay. It's main function is to handle the load that the small light switch should not. Check for power at the yellow/white lead with the ignition and light switch turned on. The relay should also click audibly when the light switch is turned on. At this point, you don't know whether the relay or the switch is the problem.
I am having the same problem on a 76 DO. I checked the power at yellow/white lead with ignition and switch on and nothing. Also no click on relay. How do I determine if I am buying a switch ?
Thanks
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